Carbon monoxide fixation by plants. (1974)

Unexpected Diversity of Bacteria Capable of Carbon Monoxide Oxidation in a Coastal Marine Environment, and Contribution of the Roseobacter-Associated Clade to Total CO Oxidation

Joe Dwyer

<a href="https://youtu.be/aqk2Xkfitas"><img src="Touch_Mars_videos/video28xna.jpg" width="560" height="315"><br> (click to watch on YouTube)</a>

First, a quick recap. We saw in Life in the clouds of Venus (above), there are a few interesting hints suggesting life, observations that could be interpreted as evidence of indigenous life. The most intriguing of these are, the presence of OCS which on Earth would be strong evidence for life. On Venus however it is just suggestive, not conclusive. There are processes that could create the observed levels of OCS without life, and detailed models of these processes are compatible with the observed levels. The atmosphere is also not in equilibrium, as it has both H₂S and SO₂. This disequilibrium is something that life could exploit. The upper atmosphere of Venus also seems to have particles that are microbe sized, and non spherical, which might be Venusian microbes.

Mars has frequent dust storms, starting with the type A storms which form in the northern autumn, travel south, cross the equator into the southern spring and then expand around much of the southern hemisphere. The year continues with the type B storms restricted to the southern polar regions, then the type C storms which are similar to type A but more variable. From time to time it has a global dust storm. These typically start in the south, during the southern spring or summer, encircle the planet in southern latitudes then extend north across the equator and can cover much of the planet. (see page 129 of this article)

Every decade or so, spread to cover the entire planet, and then can last for weeks. These global dust storms block out the sun and turn day into night, and it takes months for all the thick clouds of dust to settle back out of the atmosphere.

The first storms in the Martian year are "type A" storms from the north, forming in the northern autumn and then travel south, cross the equator into the southern spring and then expand because of the warming effect of the extra sunlight, which is absorbed by the dust and that boosts the speed of the winds, which then lift more dust expanding the area of the storm. They expand rapidly in a period of a few weeks, then persist for months.

The next type of storm, type B, start around the south pole. These reach their peak in the southern summer solstice, mid summer, they remain in the polar regions.

Then finally the last type of storm, type C are very similar to type A, but start in the northern winter, southern summer, and are much more variable.

The global storms are less well studied. They typically start in the south, during the southern spring or summer, encircle the planet in southern latitudes then extend across the equator (see page 129 of this article) and can cover much of the planet.

If it turns out that Venusian life is based on XNA, this does not make it safe for Earth life. Yes, as some say, the XNA would not be adapted to Earth life. But the other way around, Earth life might not recognize XNA as potentially harmful (as in the Lederberg quote above).

Also, adaptations of microbes are usually in the direction of keeping the host alive for longer; it is of no benefit to a microbe that infects a human for the human to die. It might also be able to out compete Earth microbes in their own habitats, and yet behave differently from them, transforming ecosystems. It could damage crops or animals, or change the balance in the seas. In the worst case, XNA based life might prove to be better than DNA based life all round. For instance it might be more efficient at metabolizing and reproducing. The very worst case is goodbye DNA. For these and other reasons, then researchers in the field of synthetic biology, who are actually contemplating the possibility of creating new life based on XNA instead of DNA (by substituting XNA for DNA in a cell, complex process but most of it is now worked out) - they are exceedingly cautious about the research.

Only 1% of the bacteria on Earth can be readily cultivated in culture media. There are various reasons why this might be the case. See Strategies for culture of ‘unculturable’ bacteria for an overview.

The "Great Plate Count Anomaly" - if you cultivate cells in a medium and count the number of Colony Forming Units (CFU's), and if you then take the same sample and count individual cells in a high powered optical microscope, typically you find that there are about 100 times as many cells as you detected with the CFU method. This is because biologists currently can only cultivate 1% of living cells, typically.

Also, only a tiny percentage of all species have been studied in any detail. So it is hard to say for sure what the capabilities are of the micro-organisms we haven't yet studied, such as the majority of the archaea. This is the issue of "Microbial dark matter". For instance a recent study found that - "Of the 100 major branches, or phyla, of microbes, less than one-third have any described species", see How Many Microbes Are Hiding Among Us?

The microbes carried by humans can have hidden extremophile capabilities - because microbes do not lose their capabilities, usually, when they move to a different environment. Some are polyextremophiles able to live in a variety of extreme environments as well as in much more ordinary ones (for humans). A typical human has 100 trillion microbes in 10,000 species - and the species mix varies from one person to another. Many of these will be unknown to science, and some may well have extremophile capabilities. For example a recent study of microbial populations of human belly buttons found a couple of species able to thrive in extreme cold and extreme heat. Another example is the discovery of a microbe on a human tongue able to thrive in conditions of very low pressure.

If it had life in the past, Dirk Schulze-Makuch and Louis Irwin suggested one other place it could survive as well as the cloud tops. It could also survive in high pressure subsurface habitats with supercritical liquid water.

If these objects do exist, they could be rather hard to spot. Water has an albedo of only 0.1, darker than worn asphalt. That may surprise you, but if an ocean is seen from above, the thing is that much of the light is reflected back along the path it came from as a specular reflection - glints of highlights. The rest is much darker.

Glint of the sun off the Pacific ocean as seen from space - view of Earth from Himawari 8. (I used a snapshot from the live view here) - water has a low albedo of only 0.1 - seems brighter because of the reflections of sunlight off it.

If there are these liquid hydrogen oceans you'd get specular highlights of the sun in the ocean which similarly would reduce the light from the planet received back on Earth.

This was a question for Quaoar when it was first discovered, in that case they were thinking about an icy surface:

" If Quaoar instead has a surface with a strong specular reflection, it could have a much smaller half-total light diameter and actually be larger. The true limb-darkening function of such an icy outer solar system body is unknown."

So in a similar way - if you had a reflective liquid hydrogen ocean with a specular highlight, it might seem much smaller than expected for the size of the planet, and so lead to astronomers to find it hard to spot the worlds and to under-estimate their size when first discovered (though occultation observations would let them measure their true size).

"It is no use arguing that samples can be brought back safely to Earth, or to a base on the Moon, and thereby not be exposed to Earth. The lunar base will be shuttling passengers back and forth to Earth; so will a large Earth orbital station. The one clear lesson that emerged from our experience in attempting to isolate Apollo-returned lunar samples is that mission controllers are unwilling to risk the certain discomfort of an astronaut – never mind his death – against the remote possibility of a global pandemic. When Apollo 11, the first successful manned lunarlander, returned to Earth – it was a spaceworthy, but not a very seaworthy, vessel – the agreed-upon quarantine protocol was immediately breached. It was adjudged better to open the Apollo 11 hatch to the air of the Pacific Ocean and, for all we then knew, expose the Earth to lunar pathogens, than to risk three seasick astronauts. So little concern was paid to quarantine that the aircraft-carrier crane scheduled to lift the command module unopened out of the Pacific was discovered at the last moment to be unsafe. Exit from Apollo 11 was required in the open sea. There is also the vexing question of the latency period. If we expose terrestrial organisms to Martian pathogens, how long must we wait before we can be convinced that the pathogen-host relationship is understood? For example, the latency period for leprosy is more than a decade. Because of the danger of backcontamination of Earth, I firmly believe that manned landings on Mars should be postponed until the beginning of the next century, after a vigorous program of unmanned Martian exobiology and terrestrial epidemiology. "

Phase diagram from this paper - though it differs in critical point and triple point saying triple point 20 K and critical point 32 K.

There is one very exotic possibility mentioned in chapter 6 of The Limits of Organic Life in Planetary Systems and that is of a solid phase of life in ice itself surviving off ionizing radiation.

As an alternative, Louis Allamandola and Douglas Hudgins considered the possibility that compounds made in ice might have initiated a Darwinian process within the comet. Indeed, a weird life form might reside within solids in the Oort cloud living in deeply frozen water, obtaining energy occasionally from the trail of free radicals left behind by ionizing radiation, and carrying out only a few metabolic transformations per millennium. While such a life form would presumably metabolize slowly, it would not necessarily be constrained by the lifetime of an associated star.

To find out more see their paper here.

"There is also the vexing question of the latency period. If we expose terrestrial organisms to Martian pathogens, how long must we wait before we can be convinced that the pathogen-host relationship is understood? For example, the latency period for leprosy is more than a decade. Because of the danger of backcontamination of Earth, I firmly believe that manned landings on Mars should be postponed until the beginning of the next century, after a vigorous program of unmanned Martian exobiology and terrestrial epidemiology. I reach this conclusion reluctantly. I, myself, would love to be involved in the first manned expedition to Mars. But an exhaustive program of unmanned biological exploration of Mars is necessary first. The likelihood that such pathogens exist is probably small, but we cannot take even a small risk with a billion lives. Nevertheless, I believe that people will be treading the Martian surface near the beginning of the twenty-first century. "

As Carl Sagan wrote:

"It is no use arguing that samples can be brought back safely to Earth, or to a base on the Moon, and thereby not be exposed to Earth. The lunar base will be shuttling passengers back and forth to Earth; so will a large Earth orbital station."

I also think that for the same reason (apart from the forward contamination issues) we shouldn't send humans to Mars until we understand Mars conditions very well indeed and have done a reasonably complete biological survey of the planet, or for some other reason have a high level of confidence that there is no life there, or that any lifeforms there are safe not just for humans, but for the environment of Earth.

That is, unless the humans are not going to return to Earth ever, which has considerable logistic issues. Also, even in that case, like"Mars One" can you hold them to that as a requirement? What if they have the opportunity to return later on and want to avail themselves of it?

Example of Apollo sample return

This is clear from Apollo. They felt it was unacceptable to leave the astronauts bobbing in the ocean, getting seasick while the world watched, they sent a helicopter with divers, who took the astronauts out of the module (dressed in biocontainment suits, but suits that had been exposed to the dusty environment inside the module), into an open boat, with the command module hatch door open to the sea. By then planetary protection was already compromised, even as assessed by the standards of their time.

From this example to show how mission planners were ready to waive precautions just to prevent the astronauts from getting seasick for a few hours while they fixed the problem, it's clear that they would definitely not let their heroic astronauts die in the quarantine facilities if they became seriously ill. If that's the way of it, then quarantine becomes a largely symbolic gesture which does nothing to protect Earth from the unlikely case of any real hazard.

You can also buy the book on kindle as a way of showing your support and appreciation. Every sale boosts its ranking in the kindle bookstore temporarily. For instance, two or three sales are enough to put it on the first or second page of best sellers for Mars, for a few days.

. In that case, one might have an understandable sense of urgency, that we don't have time for checking to see what effect we will have on Mars. The loss of the possibility of great gains in human understanding of biology, and perhaps future billion dollar industries that may be based on discoveries about Mars life - all that also would pale into insignificance in comparison with this desperate need to get humans there as soon as possible to ensure survival of our species. That seems to be the main implied narrative of those who advocate rapid colonization to create a backup of Earth in space.

Or they might be scared that we will lose our space capability in the near future, so that this is our only precious window in time to colonize Mars right now before we lose the ability to do this. But realistically -if we lose space technology on Earth - do you think Mars would retain it? As the most technological colony ever surely they would be the first to succumb if our ability to maintain complex technology disappears somehow.

I'll look into terraforming in detail later. However however you slice it, if it did work (which I think is controversial) you are talking about a thousands of years project to warm up an entire planet using planet sized thin film mirrors - or hundreds of powers stations on Mars and mining cubic kilometers of fluorite ore to generate the greenhouse gases - that's one of the "Easy solutions" to terraforming Mars.

Instead of putting that massive technological effort into terraforming Mars, why not use it to protect Earth? Build large infrared space telescopes to spot comets at great distances and do a complete survey even of the long period comets. That would be easy to achieve for far less effort thanAnd with such future technology of course we can protect Earth even from large comets.

Meanwhile, for much less cost than a vast attempt at terraforming Mars, or an attempt at a colony of a million people there, we could devote all that energy instead into protecting Earth, finding potential impactors, and deflecting them if necessary. Even Hale Bopp could be deflected if we had detection of it decades in advance with just a kinetic impact, especially with the spaceship capabilities Elon Musk envisions for Mars colonization. You only need a couple of centimeters per second delta v to deflect a comet enough to miss Earth a decade later. Suppose for instance that we did have Elon Musk's 100 person colonization spaceship. He talks about a cargo to Mars of 450 tons. Hale Bopp would hit Earth with a velocity of 52.5 km / sec. It has a mass of 1.9×10¹³tons. Suppose we achieve a relative velocity of 10 km / sec. Then the delta v would be 10,000*100*450/1.9×10¹³

I expect you to jump to the sections that interest you rather than read the book from start to end. To make that easier I sometimes repeat the same points in different sections, but keep the repetition to a minimum. Anything major, I put into a separate section and link to it, for instance there is only one section on In situ instrument capabilities for astrobiology, in the Europa and Enceladus section and I just link to it in the Mars section.

superresolution microscopy.

Can intact DNA based life find its way into the oceans of Europa and Enceladus after a meteorite impact?

Astrobiologists have designed many exquisitely sensitive instruments like this, that they want to send to Mars to do in situ searches for biosignatures. Curiosity would not be able to detect life in the low concentrations expected for either past or present day life there. And indeed, so far we haven't sent any instruments to search for life directly on Mars since the two Viking missions in the 1970s. Who knows

Especially since our life could make it extinct. About half of Earth's biological history in terms of gene complexity is unknown to us. We just have no idea how the early organic chemicals developed into lifeforms as complex as the simplest microbes. Lot's of sketched out suggestions but no answers and it is way beyond any attempt to simulate in a laboratory.

I’ve never seen this suggested for a way to keep Europa and other interplanetary landers and rovers sterile, but it sounds as if it should work!

Another issue of course is the one of sterilizing our rovers to visit habitats such as the RSLs on Mars which they can't visit at present. Perhaps if we can solve the problem of 100% sterile rovers, that could help as well by opening up the likely habitats on Mars, Europa etc to exploration without concerns that we may introduce Earth microbes to them. See Can we achieve 100% sterile electronics for an Europa, Enceladus, Ceres, or Mars lander? (above)

But for Europa, we still know very little about what might be the most interesting astrobiological targets there.

They all have similar issues, except for Titan. We have no idea whether they are all of huge astrobiological interest, or none of them, or only one or two. Astrobiological discoveries from one of them may fill in gaps in our knowledge from the others.

That's because these missions help and reinforce each other. We have already learnt a lot from Cassini's exploration of Enceladus that will help with Europa missions. In the same way Europa missions will help with Enceladus. Both may help with Titan. We are developing instruments, and spacecraft to do similar things. Also, as far as we can tell at the moment, all three of these targets are of roughly equal levels of interest, for astrobiology.

So, is this right? Is it possible to achieve 100% sterilization by heating electronics that’s capable of resisting temperatures of up to 300 °C? I don't see why not when it is already considered as a possibility for Venus surface missions. I wonder if anyone working in the field of spacecraft sterilization has investigated this, either experimentally or in theory. Or is there some other way to achieve 100% sterile electronics such as the CO₂ snow approach (see above)? If you know of any research into 100% sterile spacecraft for space exploration - do let me know and I'll include the material here!

I think we need to look into that myself before we consider sending any probes to habitats that may include liquid water habitable to Earth life. Except of course for the plume flybys. They are safe so long as the ice particles they collect can’t dislodge microbe spores and return them to the liquid water in the subsurface oceans. That sounds likely to be for all practical purposes, zero risk though you’d need to examine it carefully of course.

There's also the idea of a mobile lander in the form of the Enceladus Lander for Mobile Observation - a hopper for Enceladus exploration on the ground.

- broken link. Not in archive.org. Could contact https://www.linkedin.com/in/nicholas-hobar-946aa4a2/

I'd like to add one more speculation here. Might future deep space missions use inflatable solar panels. These are much lower mass for the same area, and they are currently being developed for cube sats, because you have limited space, only a cube 10 by 10 by 10 cms to fit them into. They would inflate into a large solar panel and mass 1 kilogram. This is the LISA-T (Lightweight Integrated Solar Array and Transceiver) under development in the NASA Marshall Space Flight Center. For cubesats, the idea is to use a double cone shaped or torus or similar shaped large inflatable solar array so that the cube sat doesn't need to point at the sun to get solar power. Their generation II prototype would generate 50 - 60 watts stored into a single cubesat unit of 1,000 cubic centimeters, including electrical cabling, deployment overhead, etc. That's a power density of 275 kilowatts per cubic meter. The mass is one kilogram.

In the 2008 study then the power system for their example Saturn orbiter is 48 kW at 1 AU, so that would requrie 1000 kilograms of mass, and for an omnidirectional inflatable LISA-T system.

- is no better than normal solar panels for going further afield in mass to power ratio. Compare 2008 study

This is one of the models of the surface processes leading to the plumes. Vapour and salty liquid droplets rise and condense near the surface and the latent heat of condensation keeps the water near the surface warm. So, in this model, there may be liquid water near the surface, kept liquid by the latent heat of condensation of the vapour from below.

Diagram of geysers

In their plan it uses a series of gravity assists from Ganymede, and Callisto, to approach Europa slowly - but use it to get an orbiter into a temporary orbit around Europa, perhaps a retrograde orbit, with very low relative velocity, then dip low to sample the geysers. (Since Europa is tidally locked to Jupiter, it makes sense to use the more stable retrograde orbit around Europa). It would have to be hardened to resist the ionizing radiation from Jupiter, but we save a lot of mass if it's an orbiter that doesn't need the sky crane to land on the Europa surface.

Sustained eruptions on Enceladus explained by turbulent dissipation in tiger stripes

In the model, the slots are mostly filled with water, and Saturn tides drive turbulent water flow in the slots whose dissipation produces enough heat to keep slots open. In turn, long-lived water-filled slots drive a volcano-tectonic feedback that buffers the rate of volcanism to approximately the observed value. Our results suggest that the ocean–surface connection on Enceladus may be sustained on million-year timescales.

He could transport the 100 colonists to Mars, at the cost of their house, but after that, they are on their own, any habitats, spacesuits, maintenance, all imports from Earth, their means for making air, water, food, they have to find out of their own pocket. How could they find even a tiny fraction of that billion dollars per year per astronaut for maintenance of the ISS?

It's a little hard to see how he could even support himself there. They are on their own. If they have to pay for everything themselves, it would seem they have to be as successful as Elon Musk and indeed, probably more so, just to have a chance of surviving there

So, it's going a little too far to say that if there is life there then it would be possible for an optical microscope with a resolution of 0.2 microns to see it at all, never mind see any detail in it. Some have suggested that even on Earth we might have cells that are smaller than that, based on a different biochemistry, the nanobes, though these ideas don't seem to have been confirmed and most think they don't exist here. But they may well exist on Europa, and whatever simpler form of life predated DNA, then if it isn't here any more, then DNA life must have made it extinct or replaced it in one way or another.

, and if the cells are either dead, or else they are in a deep state of dormancy or slowly metabolizing and requires months or years of nutrition to "wake up". Or indeed are not cultivable in the conditions provided for them

So, first, it's unlikely to land close to a geyser unless already discovered or they are very common on Europa. Also, it's only going to have a surface lifetime of 20+ days which isn't a lot of time to find out much about the frequency of eruptions, not the larger ones anyway. Hubble spotted eruptions in 2014. Jan 26, Mar 17, April 4, only three times out of ten observations that it made to search for them. Based on that, there may be a 70% chance that our lander doesn't see the plumes at all. Surely the multiple flyby mission is the way to find out about Europa plumes?

They talk about the plume material as the best place to search for life. But if that is so, surely that means that a plume sampler is the way to go, not a lander? It just seems back to front to send a lander to Europa as a way to prepare for a later geyser sampling mission, as well as its planetary protection issues.

Once we find them, then yes, a lander could be a useful way to monitor them, but only if it has a reasonably long lifetime. A 100% sterile lander on Enceladus could be a good way to keep an eye on its plumes, as they erupt continuously. Perhaps that may also be useful on Europa but it would depend on it having at least some geysers that are "Old Faithful" type geysers that erupt frequently in the same place, because of the problem of most geysers being likely to be beyond the horizon or at least at distances of hundreds of kilometers from the landing site. This may well be a good use of a sufficiently sterile lander on Europa in the future but surely this is a rather early stage for it. Surely this ground based approach to monitoring geysers belongs to a later stage of exploration, similar to the stage we have reached with Enceladus or indeed, rather advanced over it? Irrespective of whether we can sterilize the lander.

https://en.wikipedia.org/wiki/Iron%E2%80%93sulfur_world_hypothesis

William Martin and Michael Russell suggest that the first cellular life forms may have evolved inside alkaline hydrothermal vents at seafloor spreading zones in the deep sea.^[23]^[24] These structures consist of microscale caverns that are coated by thin membraneous metal sulfide walls. Therefore, these structures would resolve several critical points germane to Wächtershäuser's suggestions at once:

the micro-caverns provide a means of concentrating newly synthesised molecules, thereby increasing the chance of forming oligomers;
the steep temperature gradients inside the hydrothermal vent allow for establishing "optimum zones" of partial reactions in different regions of the vent (e.g. monomer synthesis in the hotter, oligomerisation in the colder parts);
the flow of hydrothermal water through the structure provides a constant source of building blocks and energy (chemical disequilibrium between hydrothermal hydrogen and marine carbon dioxide);
the model allows for a succession of different steps of cellular evolution (prebiotic chemistry, monomer and oligomer synthesis, peptide and protein synthesis, RNA world, ribonucleoprotein assembly and DNA world) in a single structure, facilitating exchange between all developmental stages;
synthesis of lipids as a means of "closing" the cells against the environment is not necessary, until basically all cellular functions are developed.

The Sounds of Europa and press release

“We can also sort out high frequency signals from longer wavelength ones. For example, small meteorites hitting the surface not too far away would produce high frequency waves, and tides of gravitational tugs from Jupiter and Europa’s neighbor moons would make long, slow waves.”

The sound of Europa? Garnero adds:

“I think we’ll hear things that we won’t know what they are. Ice being deformed on a local scale would be high in frequency — we’d hear sharp pops and cracks. From ice shell movements on a more planetary scale, I would expect creaks and groans.”

“We want to hear what Europa has to tell us,” adds Hongyu Yu (ASU School of Earth and Space Exploration), who heads up the project. “And that means putting a sensitive ‘ear’ on Europa’s surface.”

The report suggests many interesting ways to search for life on the Europan surface, especially ideas involving microscopy. However it is also rather controversial in some ways, especially in its recommendation

s to prioritize experiments based on biochemistry over ones that detect metabolism. Then there are many issues with searching for life on the surface of Europa, including, whether it is present at all, whether it is highly degraded, whether it could be too small to see, and what if it is mixed up with other types of organics? So I go into that in some detail.

The next few sections may get a little technical for the general non scientific reader. There was so much of interest to discuss in this report and I felt it would cheat the reader not to at least touch on some of these points. It's on a similar level to, say, New Scientist or Scientific American - that you aren't phased by a few chemical equations and ball and stick models for organic molecules. If you don't have that background, you can still read it and skip the more techy parts. Or if you want to skip this next section altogether, you can jump ahead to How easy is it for Europan life to reach the surface?

The basic points in the next few sections are that the report presents many interesting ways to search for life on the Europan surface, especially the ideas involving microscopy. Ho

Many scientists think the key to studying Europa thoroughly in the future will be to send an ice mole or a submarine. Steve Squyres, lead scientist for NASA's Opportunity rover on Mars in 2012 describes a Europa submarine:

"This is fantastic stuff, This is the holy grail of planetary exploration right here."

It's not like geology in that respect. We don't yet know what we are looking for, where it is likely to be, or what the best instruments are to use to find it. We can't detect it remotely and it can be very localized. As for Mars, the best way to find traces of life might be a lander that's able to move, and to drill deep to avoid the ionizing radiation.

However, we'll see that it doesn't seem too likely that it would be able to detect Europan life. It could only do that if its remains on the surface are rather astonishingly abundant, cover large parts of the surface (since we don't know much about how to intelligently select a landing site), are relatively undamaged by the intense radiation from Jupiter's ionosphere, easily separable from meteorite and comet organics that must cover the surface, and easy to recognize.

As they say at the head of the report,

"This mission would significantly advance our understanding of Europa as an ocean world, even in the absence of any definitive signs of life, and would provide the foundation for the future robotic exploration of Europa."

The rest of the Europa lander report is similar. They were told by the politicians that it had to be a lander, and even told what the launch date would be as well. It wasn't in their remit to discuss the timing for a lander on Europa., or the possibility of a gesyer flythrough instead. Even if they had wanted to do a comparison study on a geyser flythrough with a lander (who knows, maybe some of them would), it simply wasn't in their remit to make that comparison, and they don't attempt to discuss relative mertis of a lander over a geyser flythrough anywhere in the report..

That's what happens when you have politics directing the goals for a science mission. You end up with the politicians setting the remit for the scientists. With such a remit, there is no way they could recommend a geyser flythrough.

With this background, it's a natural response to highlight passages in earlier reports that recommend a lander. But if you read the sources themselves, though they do mention a lander, they also rather clearly favour orbital study and geyser sampling over a lander, at this point in time. The lander is seen as a useful future mission, so what they said was correct, but it is seen as most useful for a rather later stage in exploration of Europa.

They suggest several methods for searching for Europan life, in the report, but they all have the drawback that they need a reasonably clear signal, and would struggle if faced with degraded organics, especially if they are also mixed up with organics from comets and meteorites. They will be hoping to find biosignatures of life that are either very obvious, or also easily separated out from the other organics, and or not mixed up with anything else. That could be life that was recently in the subsurface oceans, or from some other environment of interest as a habitat for the search for life or prebiotic chemistry in the surface ice - a microhabitat, or a larger subsurface melt lake.

See How Self-Replicating Spacecraft Could Take Over the Galaxy.

- I think it might be fair to add the idea that they are hibernating until the universe cools down enough for their computers to work more efficiently to allow them to make the best use of resources in our universe - a preprint for the article itself is here. An earlier similar idea is that advanced civilizations might migrate to the outer rim of the galaxy where the background temperature is lower, for the same reason.

It's not enough to recognize the microbes as a threat, our defenses also have to be active and respond, to stop them from causing harm as well. So, that leads to a thought (not in the sources I read). If what we have is an unusual form of biochemistry, could the attempts by our defenses to annul the threat actually make things worse, for instance provide the microbes with chemicals that they find useful, as food or in other ways, instead of harming them? There are examples of this in nature. Maybe I'll find a better one, but birds often pick up ants and rub them on their body for "anting" - it seems that the formic acid they produce as defense is beneficial to them in some way, perhaps to help remove parasites. If that's so, then the more formic acid the ants create as defense, the better, as far as the birds are concerned.

It would also violate the nuclear test ban treaty (would it be possible to negotiate a "peaceful use" exemption?). However, what happens if it blows up on the launch pad? The bombs also are "self actuating" which means a proliferation risk if they are stolen. Also, even with the nuclear fusion bombs designed to be as clean as possible, with a nuclear bomb exploding every three seconds, it will still be a fair bit of radioactive fallout.

It's perhaps not completely ruled out as a method for travel. In the conclusion to Nuclear Propulsion: Orion and Beyond, the authors suggest that it could be redesigned to use compression of subcritical fission material, and be a way to dispose of our nuclear weapons-grade fissionable material. If there was a need to transport large payloads through the solar system, we could use this method in space (though not for the launch from the Earth's surface), exploding the nuclear material in the vastness of interplanetary space where the radioactive debris is not an issue.

https://arxiv.org/pdf/astro-ph/9901322.pdf%3Forigin%3Dpublication_detail

"Once an interstellar spacefaring civilization develops, it should sweep across the galaxy like wildfire, as viewed on galactic timescales."

An Astrophysical Explanation for the Great Silence - intro is quite good though it suggests gamma ray bursts would sterilize the host galaxy, no longer a hypothesis for them.

https://phys.org/news/2009-06-galactic-colonization-limited-inability-exponentially.html

new take on the Fermi Paradox, though, changes the equation a bit. At Pennsylvania State University, two scientists suggest that the key to the paradox is the assumption that civilizations would colonize the universe at an exponential rate. Jacob Haqq-Misra and Seth Baum point out that finite resources preclude exponential expansion.

"The problem is that this kind of growth may not be possible, and they look at Earth as an example. For any expansion to be sustainable, the growth in resource consumption cannot exceed the growth in resource production. And since Earth's resources are finite, and it has a finite mass and receives solar radiation at a constant rate, human civilization cannot sustain an indefinite, exponential growth."

This means that, if we decide to colonize our galaxy, Earth's civilization will be unable to do so at an exponential rate. If you apply the realities of Earth to possible alien civilizations, then it becomes much more likely that there are other advanced societies out there. Like Earth, though, they are limited in their expansionary capabilities. Perhaps there are thousands of alien societies out there, just trying to effectively colonize their moons or settle on planets in their solar systems. It is possible that, if that is the case, the question of existence of intelligent alien life may not be answered in our life times.

Anyway after this aside, looking at other places to search for life in the solar system, and other places where humans could live too apart from Earth and the Moon, let's go back to Mars. Though it's certainly not the only interesting place for humans and rovers to go in the solar system, or the closest (both Venus, including its clouds, and the Moon are closer), there's no doubt that at present it has quite a hold over the popular imagination. And there is a lot about it that's of interest to us, for sure.

More generally, looking further into the future, habitats on the Moon would probably be just a first step. Suppose we do find a way to have millions living in space - I argue in my Moon First books that settlement in space has the potential to be hugely positive but it could also be hugely negative. It depends very much how it is done, and it may well turn out to be a good thing that we are likely to have comparatively few humans in space to start with.

Though I'm keen on humans in space, I'm no advocate for sending large numbers of us there as fast as possible (except as explorers and tourists). In any group of millions of people you may start to get some with strange and even destructive and violent ideologies, similarly to North Korea or ISIS. If a space colony develops such an ideology, they have space technology far advanced over ICBMs. We may get many peaceful, positive ideologies in space, but others might turn out to be as extreme as anything we have had on Earth so far, or maybe more so.

So, if the violence we get on Earth propagates into space, how can humans remain in space for long? Any habitats in space will be so fragile to violent actions, that even lobbing a rock at them at a few kilometers per second, an easy thing to do for any group of millions of people with space technology. With no air to breathe, there'd be no possibility of survivors hiding out in caves. If their environment control, hull integrity, or spacesuits are destroyed by the blast, how can they survive?

With hundreds of thousands, and millions of people in space - how can we restrict space colonization to the "good guys or gals" whoever we think those would be? So, let's not rush into that future. Slow and steady may win the race here.

Humans in habitats at the Venus cloud tops

There's one other main possibility, which I should mention, which Seth Baum suggests in his conclusion to The Sustainability Solution to the Fermi Paradox

" It is also possible that faster-growth ETI civilizations previously expanded throughout the galaxy but could not sustain this state, collapsing in a way that whatever artifacts they might have left have also remained undetected. Both of these growth patterns can be observed in human civilization, suggesting that they may be possible for ETI civilizations as well."

However, whatever may happen around other stars, our own solar system shows that there would have been pristine refuges for the ETIs to retire to, to evade the hazard, whatever it is. It can't be that they ran out of resources, because there is no sign that they even tried to utilize resources in our solar system. And as for a weapon targetted only to destroy their own kind, or sterilize them to make them unable to reproduce, surely over the 100,000 years it takes to cross the galaxy, they would find a solution and a way to fight back and recolonize the galaxy?

It's hard to see how anything could make a galaxy spanning civilization extinct. Unless they, or some other extra terrestrial, have FTL travel. In that case, maybe...

I wilI suggest that once a civilization spans a galaxy, it is immune from extinction, for as long as the galaxy remains habitable, except by being overrun by successor self replicators that out compete it. If so, their successors would still be here. So there could be ancient artefacts and ancient extinct civilizations, yes, but there would also be present day civilizations.

That is - unless they were destroyed by robots? That's possible. Perhaps a more advanced civilization, though confined just to a small part of the galaxy, sees this galaxy spanning civilization as a risk to the galaxy, and finds a way to trigger it's collapse galaxy wide, using self replicating robots.

They could also have artefacts throughout the solar system with For this scenario see my Self Replicating Robots- Safer For Galaxy (and Earth) Than Human Colonists- Is This Why ETs Didn't Colonize Earth?

Were we just lucky? Do extraterrestrials sometimes become extinct after their first Apollo style mission to their nearest Moon or planet? (above)

This is based on zero data about extraterrestrial biology - so doesn't that mean we can ignore the risk?

? North Korea claim to have space aspirations and have put a satellite into orbit, though most consider it to be a cover for ICBM research. Also North Korea is not expansionist, but is developing ICBMs to protect itself (see my Tense situation concerning North Korea for some of the background, with links to sources).

However, in the future with improved technology world wide and millions in space, then perhaps such governments will have the ability to set up their own colonies, and maybe they avail themselves of the opportunity. Also, w

Potentially habitable exoplanets in the Planetary Habitable Laboratory's conservative list of habitable exoplanets. Artistic representations. Earth, Mars, Jupiter and Neptune for scale. Distance from Earth is between brackets. Planet candidates indicated with asterisks. CREDIT PHL @ UPR Arecibo (phl.upr.edu) May 11, 2017.

There are 39 of them in the optimistic sample. We could reach the ones within 100 light years in the next thousand years traveling at only a tenth of the speed of light with the technology we'll surely develop in the next century or two.

Actually the habitable planets might be amongst the worst to colonize, if they have native life harmful to Earth life, or that we don't want to make extinct, though amongst the best if reasonably compatible. That doesn't much matter though. We could colonize almost any star system, if we fill their habitable region with Stanford Torus type settlements using materials from their asteroid belts and Oort clouds, with a colonizable "surface area" inside all those habitats equivalent to thousands of times the land area of Earth. There is no shortage of places to colonize with near future technology. Wikipedia (which is quite good on this topic) currently lists 60 hydrogen fusing stars within 16.3 light years (5 parsecs) of us.

Also, any lander needs to be hardened for the ionizing radiation for Europa and hardening for ionizing radiation has some similarities to hardening for high temperatures. So adding a requirement to be 100% sterile might not be such a huge change.

Apart from that idea, perhaps we can downplay it a bit, not so much "betting the ranch" on the most perfect sample return ever? We don't ask it to pick up all the caches, so saving maybe an extra year or so of travel time (bearing in mind that it then has to return to the MAV at the end). This also reduces the launch mass back to Earth.

The main problem there is that it needs the witness samples and blanks in order to help assess the amount of contamination. So our sample retrieval system has to pick those up. But perhaps the half dozen best of the remaining samples?

Then for the return from Mars orbit, sterilize the sample so you don't have the legal complexities or the costs of a Mars receiving facility and makes the whole thing simpler. That is, unless we already have very clear evidence of life within it. If there is clear evidence, then I think the extra funding for handling that should be easy to obtain, and return to above GEO and split it there and sterilize materials to return to Earth, as in my above GEO suggestion.

This wouldn't have the astrobiologists behind it so enthusiastically. But it would cost less because you return less mass, which reduces the cost and complexity of the MAV. Also by sterilizing it, then you remove the complexities and costs of a Mars Receiving facility, while still preserving any astrobiological value it may have for past life, leave some possibility for detecting sterilized extant life, and preserve its geological interest,

All this could easily trim a billion dollars or more (you save well over half a billion dollars for the receiving facility).

Also it means you don't have to go through the complex legal process. Though that may not be topmost on the minds of the astrogeologists - once it becomes clear that Congress will have to pass probably decades worth of laws to permit us to return this, it is likely to be an additional disincentive some time down the line.

I.e. simplify it as much as possible. And sell it as a geological mission and a technology demo. If they sell it as an astrobiology demo, it's going to be a big anti-climax if it returns samples that are as ambiguous for astrobiology as the Mars samples we already have. So it's a case of full disclosure right away, that astrobiologists see it as a technology demo rather than a way to solve the main questions in their field.

Less radically, perhaps they can keep Mars 2020 as a sample catcher. But we can downplay it a bit, not so much "betting the ranch" on the most perfect sample return ever. We don't ask it to pick up all the caches, so saving maybe an extra year or so of travel time (bearing in mind that it then has to return to the MAV at the end). This also reduces the launch mass back to Earth.

With this idea, Mars 2020 would leave caches every year or so, maybe 5-10 sample tubes. Then the scientists decide which of these is the most interesting cache for the MAV to pick up. That still fulfills the main objective of adaptive caching, to ensure that there is a sample to pick up by the end of the prime mission - and then adds additional optional caches for later on if it survives extended missions and finds more interesting material later on. It would lead to duplicate sampling, as geologists resample rocks they sampled in earlier caches that are of especial interest if they think they can now leave a superior extended mission cache. But that doesn't seem a problem, especially if it makes the difference between a mission that's possible and one that can't be done at all.

So then, you land a rover that drives to the nearest cache from a distance of up to 20 km, so within 200 days, returns to the landing site, and launches to orbit. It would return maybe 100 grams or less, instead of 450 grams. A smaller sample to return would reduce the cost of the MAV and of the mission to pick up the capsule from Mars orbit and return to Earth.

All this could easily trim a billion dollars or more (you save well over half a billion dollars for the receiving facility), as well as the complex legal process. Though that may not be topmost on the minds of the astrogeologists - once it becomes clear that Congress will have to pass probably decades worth of laws to permit us to return this, it is likely to be an additional disincentive for approving it some time down the line.

I see two main possible futures here (though with many other variations on them). One, where we find that the Mars surface is uninhabitable and humans land there just as they did on the Moon. That would be fun and exciting just as it was for the Moon. The young space geek, science fiction loving kid in me would just love that! In this future, the surface of Mars is not unlike the Moon though with more ice. It has some liquid water in the form of salty brine layers on the surface (we know that already) and in the deep hydrosphere, but none of it is habitable to Earth life, or at least none of the accessible water is habitable. Basically it's a larger Moon with more ice and some very salty uninhabitable brines.

In this future, humans could perhaps land early on .Though, it needs thought even then. There are still issues to think over about introducing earth microbial spores that could interfere with future plans to transform Mars. It is after all, an entire planet, connected through the dust storms, and the dust able to protect spores from UV light. Even if there are no habitats for Earth life, the spores would get into shadows and eventually caves and could have effects thousands of years later.

Also, though the first landing of humans there would be exciting, after the initial excitement, it might well turn into a place like any other. Humans cramped in habitats, complaining about the food and the difficulties of being cut off from Earth, posting homesick video clips talking about how they never get to see a blue sky or sunlight or trees or grass any more, how they can't get out of their habitat for weeks on end in the dust storms and complaining about how long it takes to put on a spacesuit etc etc. Earth might soon start to seem a paradise to them, that blue planet where there is abundant water and breathable air everywhere, temperatures just right for life and you can walk anywhere without a spacesuit and feel the sunlight and rain and wind on your skin. Living on Mars would probably seem a lot more mundane than it does at present in science fiction stories and movies. Like the way the general public got bored of humans on the Moon in the 1970s.

The other future is one where the Mars surface turns out to be habitable to Earth life, and so to native Mars life too, if it exists. In the most exciting future here, perhaps nearly all those suggested habitats turn out to be habitable. Nilton Renno's salt / ice interfaces, the seeps of briny water, the pure water at 0 °C in Richardson crater due to solid state greenhouse effect through pure ice, it has lichens and other lifeforms on the surface using the 100% night time humidity, lifeforms in the Hellas basin, all of those inhabitable. Perhaps even, it's a planet with multiple genesis, not just one "Shadow biosphere", but several, all co-existing, basedon different biochemistries. We'd learn so much from that.

Almost anything that could happen in this future is exciting. Even Zubrin's picture of a Mars with the same lifeforms as Earth would be exciting. How could that possibly happen? How did they all get there, and when, and why didn't they evolve in some different direction from their cousins on Earth? A future like that with uninhabited habitats would be interesting too. We'd learn a lot from both these futures.

The most thrilling future of all here, though, would be the discovery of indigenous life or early life precursors. Mars has such a different past from Earth, at its most habitable for just a few hundred million years, with oceans, early life could have evolved there and still be there. Those early life forms might never have gone extinct on Mars. Wouldn't that be just the most amazing thing to find there? Life that was made extinct on Earth, and they could be extremely vulnerable to Earth life. That would fill in a huge gap in our understanding of life.

Or, if we were to find some form of life that's followed a totally different direction of evolution from Earth life. Even perhaps more than one form of biology, different directions explored and perhaps none of them have yet taken over as the only form of biology on Mars.

That would be like discovering an exoplanet, complete with its own extraterrestrial life, in our own solar system. Ok, in this future, humans can't land on the planet, not early on anyway. But to compensate, they can explore it by telepresence, and we can all participate, looking at the streaming feeds from Mars and walking via virtual reality through the landscapes they uncover in their explorations from orbit. It would be exciting to follow the expeditions of the telenauts exploring Mars from orbit. And there's something also fascinating about a place you can't go to in person, for whatever reason. It would add to the interest and mystique of Mars.

For me, that's by far the most exciting future here. So, though the sci fi geek in me likes the future with humans on the surface like the Moon, as someone who is dead keen on science and astrobiology, I'm rooting for that other future where the habitats turn out to be inhabited - and most exciting of all, a future with some form of indigenous life, early or life precursors or alternative biology. This is a scientific possibility at present, something that could turn out to be true. I hope this is what we'll discover on Mars in our near future.

In that future, you'd still have humans exploring in many other places in the solar system including Mars from orbit and its two moons.

You can come up with many other possible futures, and there might be other possibilities that we can't see yet.

I hope though, whatever happens, that we don't end up in a future where we accidentally introduce Earth life to Mars like the Arthur C. Clarke Venus explorers in the introduction (Why don't explorers in science fiction have these problems when exploring other worlds?). That would be so sad, to do that by mistake, as something we don't want to do, as an event that perhaps as in his story, surely future humans would think back on with sadness for those vanished species they will never be able to "meet", even through a microscope, for the rest of future time.

Or, as Rick Davis put it in a press conference, “Human beings are, roughly speaking, about 50 percent microbes by mass. We’re basically, if you will, big sacks of microbes. And so keeping that segregated from the Martian environment when humans get there is probably impossible.”

Cassie Conley said,
“To date, there has been a consensus that everyone will follow the same rules with the objective of conserving these things for future generations. From what I can tell, this is the first time in human history that humans as a global society made these kinds of decisions. And so far for the last 50 years we’ve managed to stick with them. We’ve never succeeded in doing something like this before.”

https://www.youtube.com/watch?v=tFgkvnwflvI

As reported in Wired magazine:

"That uncertainty doesn’t bode well for Musk’s original Mars ambitions. Musk argued that the Falcon Heavy was impossible to test on the ground due to the machine’s complexity. And he said that development was far more difficult than SpaceX expected, admitting that the company was naive in its original projections. The simultaneous firing 27 orbital engines notwithstanding, launching a Falcon Heavy includes changing aerodynamics, heightened vibration, and an enormous thrust that pushes qualification levels of the flight hardware to the limit. Musk admitted on Wednesday that limited damage to former Apollo 11 Pad 39A would be a “win” in the aftermath of the Falcon Heavy test flight. Along with Musk, the audience laughed nervously."

Also, if it has a landing ellipse similar to Curiosity, 20 kilometers by 7 kilometers then it may be up to 20 kilometers away from the first sample to collect, which at 100 meters a day means 200 days to get to it. With Curiosity 2020 they hope to improve this to a diameter of 10 km. by using "range trigger" - it decides when to release the parachute in order to reach closer to the target instead of releasing it at the earliest opportunity as in all missions to date. That makes it maximum of 100 days to get to it. It would take a similar period, 100 days, to get back to the MAV, or to rendezvous with a separate MAV. Or, if they target the cache itself at the center of their landing ellipse, then it has to travel up to five km, so that's 100 days there and back.

So you are talking about a prime mission that would span more than 200 days on the surface plus probably several hundred days to follow the tracks of Curiosity 2020 to pick up the sample. So it has to get to less than nine years after the start of Curiosity 2020's sample caching, to launch the samples to Mars orbit within that ten years timescale. That seems to suggest that it has to launch by 2030, assuming Curiosity 2020 launches in n 2022. Casey Dreier and Jason Callahan say in their report that it has to launch in the 2020s (page 22) which I presume is allowing an extra year or so to follow the traverse of Curiosity 2020 to pick up the samples.

Asked about the Falcon Heavy, he says (video link)

"How are you managing the risks associated with the Falcon Heavy, and particularly the recently announced private launch round the Moon?"

"First, I should say, Falcon Heavy, that requires the simultaneous ignition of 27 orbit class engines. A lot that could go wrong there. I encourage people to come down to the Cape to see the first Falcon Heavy mission. It's guaranteed to be exciting. It's one of those things that's really difficult to test on the ground. We can fire the engines on the ground, and we can try to simulate the dynamics of having 27 instead of 9 booster engines, and the airflow as it goes through transonic. It's going to see heavy transonic buffet. Max Q, there's a lot of risk associated with the Falcon Heavy. a real good chance that vehicle doens't make it to orbit. We want to make sure we set expectations accordingly. I hope it makes it far enough away from the pad that it does not cause pad damage. I would consider even that a win, to be honest. ".

"That dwindles the number of people who want to rid on that that first time"

"Yes, full disclosure here, I think Falcon Heavy is going to be a great vehicle, It's just like so much that's really impossible to test on the ground. We'll do our best. It actually ended up being way harder to do Falcon Heavy than we thought. At first it sounds real easy. You just stick two first stage rockets on as first stage boosters. How hard can that be? But then everything changes. All the loads change, aerodynamics totally changed, you've tripled the vibration and acoustics, if you break the core levels on so much of the hardware, the amount of load you are putting through that centre core is crazy, because you've got two super powerful boosters also shoving that centre core, so we had to redesign the whole center core airframe, It's not like the Falcon 9 because it is going to take so much load. Then you've got separation systems, It ended up being way way more difficult than we originally thought. We were pretty naive about that. But the nice thing is, fully optimized, it's about two and a half times the payload capability of a Falcon 9. Well over 100,000 pounds to LEO, you can even get up to a bit higher than that if optimized. And the nice thing is, it does have the throw capability to toss a Dragon in a loop around the Moon. The Dragon 2 itself, the heatshield is designed with a huge amount of margin. It's got enough margin to handle lunar re-entry, particularly if we do initial velocity scrub, one pass through [the atmosphere] and come in on the second pass. But no question, whoever is on the first flight, they're brave.

Humvee journey through the Arctic - contamination study

I should mention this as it is often cited, a study by Andrew Schuerger and Pascal Lee from 2010. It's often brought up in Mars colonization discussions as an example to show that you can explore the Arctic without contaminating it with microbes. If that was true, it would seem to contradict those experiences of Antarctic researchers with their heavily contaminated base camps and the corral system. Actually their result was, though interesting, somewhat more limited than that.

First, the background. These researchers drove a humvee through the Arctic, and looked at how the microbes spread out from their vehicle, which they deliberately did not attempt to sterilize in any way. They found very low levels of contamination at a distance of ten meters from the rover. They took this as a "worst case" analogue of a mission on Mars in a crewed rover.

I think it's important to realize what this study was, and what it wasn't. They were not saying that the ground around a human base would be free of microbes. As we've just seen, after a ten day camp in Antarctica following the corrall system, you'd expect a hundred thousand microbes per cubic centimeter around the camp. Spacesuits might reduce those numbers, but not to zero, because they leak, and anyway they weren't simulating the use of spacesuits.

Instead they were interested in the amount of contamination at a distance of ten meters from the rover itself and from human activities around it. They were interested in how the microbes disperse in extreme environments like that..

"The snow sampling was designed to measure the aerial dispersal of microbial cells and spores falling upon undisturbed snow within ~10m of the rover and not in its immediate vicinity. Snow and ice surfaces upon which the crew walked, prepared food, conducted science experiments, eliminated wastes, and worked on vehicle maintenance were not directly sampled. Thus, the sample design was specifically constrained to measure aerial dispersal from human activities around a contaminated rover within a 10 m radius of the crewed vehicle but not the direct footsteps of the crew."

So yes, they accept that a rover and base would of course leave a microbial footprint on Mars, but perhaps the contamination would not spread much further from the base. In particular, if astronauts set off on rover journeys across Mars, it might have less microbial impact than you'd expect. They were studying specifically "early sortie missions in pristine environments"

"Based on our results here, and the literature cited above, we propose that the dispersal of human-associated microorganisms is likely to be low during early sortie missions in pristine environments, is likely to increase slightly over time with continued exploration of a specific site, and will decrease over time once the exploration of a given site is halted. Further study is warranted for human exploration activities at temporary field sites on pristine terrains in order to characterize the temporal changes in dispersed bioloads and microbial diversity."

They suggest that in the harsh conditions on Mars, it may be possible to tolerate low to moderate levels of contamination at sites knowing that the harsh environmental conditions present will constrain long-term survival or colonization of nonindigenous species.

They suggest that UV light would sterilize the external surfaces of the spacesuits, rovers and habitats.

"Numerous studies have demonstrated extremely short survival times of viable terrestrial microbes under martian conditions and suggest that microbial contamination on external surfaces of spacesuits, equipment, rovers, and habitats will survive only a few hours to a few sols on Sun-exposed surfaces ... Although dust settling onto vehicles or spacesuits may attenuate a portion of the UV irradiation incident on surfaces, the biocidal activity of UV photons on the viable contamination is likely to be significant and accumulative because the dust does not cover the entire surface and scattering of UV photons around dust particles is likely to occur "

However, unless I'm missing something here, they don't seem to consider the effect of shadows, or the dust storms. At any moment, half of the rover at least is in shadow, same for the habitats. UV light is blocked out by a shadow, apart from any scattered light. Also there are many shadows around the rocks. A microbial spore that falls from a habitat,astronaut or rover on its shaded side and lands in a shadow can survive on Mars not just for minutes or hours, but indefinitely. The DLR experiments showed that some cyanobacteria can even "wake up" and photosynthesize and metabolize in semishade on Mars.

A microbe deep in a crack in a rock, beneath an overhang,, even embedded in a crack in a larger dust grain, will be protected even from most of the scattered UV light. Then, when the dust storm season comes, then they can be lifted up and moved almost anywhere on Mars.

Anyway - they recognize that a mission on Mars is like a mission in Antarctica, and that there would be microbial contamination around the base. Enthusiasts for Mars colonization often mention this study, saying that there was no contamination. But of course there was. You can't have a mission with humans traveling through the Arctic without a lot of contamination wherever they walked. Their result was that they found very little contamination at a distance of ten meters from the human activities. They must have left many patches of ice with thousands of microbes per cubic centimeter or more.

Sulfur dioxide can even be produced by the reaction of hydrogen sulfide with the oxygen in the air. Hydrogen sulfide is released from marshes and regions in which biological decay is taking place, as explained by David W. Brooks from the University of Nebraska-Lincoln.

http://sciencing.com/major-sources-sulfur-dioxide-10011402.html

If there was oxygen in the atmosphere it could also produce sulfur dioxide through reactions with hydrogen sulfide. Sulfur dioxide and

That is a very high level of sterility for sure. The aim is that 99% of the time the samples won't have as much as a single viable microbe in them.

They don't give any examples in the report, for this concern about microbes reproducing during the journey back. However, Mars has many deposits of ancient clays, so I'm guessing that this is what they had in mind (do say if you know more). Curiosity studied a sample of Martian clay and found it formed in conditions habitable for life. These are likely samples to return in the search for past life. Clays can hold onto water even in the near vacuum conditions of the Mars atmosphere. These can't be kept refrigerated during the sample return, giving a possibility of Earth microbes reproducing in the sample.

Still, if they do announce life in the sample, is even such a tiny chance that it is Earth life enough to make such a fr?

Presumably the chance of a microbe reproducing in the sample would be a lot less than that 1% because the microbe would also have to be able to colonize whatever material is in the sample, and also, this is a requirement and they would probably exceed requirements in practice. Still, even with these low probabilities, I think this means that if they found viable life in the sample, then the first assumption would be that it came from Earth. They would have to try to rule that out if there was thought to be a chance of viable Mars life in the sample. Similarly also if they found significant amounts of a biosignature in a clay that might have enough water activity for an Earth microbe to reproduce in it, again the first assumption would be contamination which they would have to rule out.

It's a similar issue for ExoMars in situ studies however. Their current plan (as of 2014) is a limit of 50 ppb for organic material from biological sources, of samples delivered for in situ life detection. Perhaps we need to find a way to achieve more sterile landers before we can do the studies of Mars organics at the levels of sensitivity required by the astrobiologists?

- not sure of this.

http://authors.library.caltech.edu/42647/1/Ming_et%20al_2013_Science_Sheepbed%20Volatiles_Accepted.pdf

Terrestrial contamination from the sample handling chain is unlikely because it was scrubbed multiple times with Rocknest scooped material prior to the first drilled sample at JK (10,9). T

Note, that their parts per trillion sensitivity requires extremely sterile sampling systems on Mars. Curiosity achieved . ExoMars (as of 2014) has a limit of 50 ppb for organic material from biological sources, of samples delivered for in situ life detection.

, except for the remote possibility of revivable ancient life, or life retrieved from pure ice, or from salt deposits with no radioactive isotopes in them.

They are still present at doses hundreds of times stronger, after 14 MGy (those are megagrays, or a million grays, not to be confused with mGy or milligrays, or a thousandth of a gray). If these are samples of early life on Mars, then 14 MGy is approximately the dose the microbes received anyway from natural nucleotides in the rocks after being preserved for billions of years in ideal conditions.

The basic issue here is that the plan is to return unsterilized samples from Mars to Earth before we know what is in them. To do that safely we have to design the sample return in such a way that the facility is safe to handle any conceivable extra terrestrial biology, before we have discovered even one other example of life other than Earth life. Then we have to pass legislation too, to take account of all the possible forms of life we could return in that way, without any data on what those lifeforms might be, or whether they can survive on humans, and whether they can harm us, or the environment of Earth. I think that's the main thing that makes this so tough.

It's not like planetary protection in the forward direction, which is legally far simpler.

To take an example of a case where we might need no precations, even for an unsterilized sample -if we find early pre-DNA life, for instance RNA world, or even almost alive prebiotic chemistry - and if we can show it was made extinct on Earth billions of years ago, then just the presence of life like that on Mars might already be good evidence that modern life hasn't arisen there. It might need more research to get to a reasonably rigorous scientific proof of this).

On the other hand if it has an advanced sophisticated biochemistry, not based on DNA or RNA at all, or if we had evidence that the life is at a stage of evolution several billion years ahead of Earth, or has capabilities Earth life doesn't have (such as more efficient photosynthesis) then everyone would agree that it might need extreme caution. In these cases, all those complexities are necessary and of course we have to go through with them.

The most recent ESF study on how to deal with samples returned to Earth from Mars recommends returning them to a new type of facility which has to contain them right down to the level of GTA's as well as the smallest size of microbe they think is possible using unknown extra terrestrial biology. Their recommendations are that it has to be capable of containing particles well below the optical resolution limit of 200 nanometers (ideally it shouldn't permit release of particles over 10 nanometers in diameter). In other words, the facility has to be able to contain particles only visible with electron microscopes or similar. This is well beyond the capabilities of a normal biohazard level 4 containment facility where the aim is to contain known hazards of known size and capabilities. It also has to protect the samples against contamination by Earth life, even by a few amino acids.

Also, there's all the extra legislation to pass.

As I said earlier, in the shorter Legal complexities summary (above), I'd go further than this. Any quarantine regulations seem especially challenging, if you consider the case where the sample is found to contain microbes potentially hazardous to Earth, and a human has been exposed to these microbes and can't be sterilizied of them.

Suggestion for protection of Earth during sample return - ionizing radiation

Martian life could be XNA, capable of setting up an independent self contained ecosystem on Earth. Martian cells could also be far smaller than Earth life, as the earliest cells before the archaea must have been at most a few tens of nanometers across, about a tenth of the size of the smallest known modern cells (the ultramicrobacteria). Or, if it has a common origin with Earth life, could have capability of transferring genetic material via Gene Transfer Agents, as archaea are able to swap material very readily in this way, and the GTA's are again only a few tens of nanometers in size.

In the XNA specifications section of this paper: Xenobiology: A new form of life as the ultimate biosafety tool The authors talk about biosafety requirements for this procedure

"The ultimate goal would be a safety device with a probability to fail below 10^-40, which equals approximately the number of cells that ever lived on earth (and never produced a non-DNA non-RNA life form). Of course, 10^-40 sounds utterly dystopic (and we could never test it in a life time), maybe 10^-20 is more than enough. The probability also needs to reflect the potential impact, in our case the establishment of an XNA ecosystem in the environment, and how threatening we believe this is."

Since XNA from Mars could also potentially set up an XNA ecosystem in the environment on Earth, we need to be similarly careful when considering its impact.

This all makes it extremely hard to contain reliably, especially when you don't yet have a thorough understanding of what it is you need to contain. It is not too bad so long as you keep the specimen in the capsule, but as soon as you remove samples for analysis, it's hard to see how you can keep it completely enclosed to ten nanometers level - as the optical resolution for the best high powered microscopes is around 200 nm. There's also the risk of damage to the capsule, and loss, theft, natural events such as hurricanes, or airplane crashes, or human error leading to accidental release.

With this background, then you can see that ideas for quarantine just wouldn't work to keep Earth safe.

But our technology is changed hugely since the 1960s, and our ideas of how to explore the solar system and how to search for life are changed too, and Europa is a very different place from Mars. And we are not thinking in terms of an "exploration phase" anyway.

For more on all this see my:

Does Earth Share Microbes With Mars Via Meteorites - Or Are They Interestingly Different For Life?
Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited
No Simple Genetic Test To Separate Earth From Mars Life - Zubrin's Argument Examined

We'll only be able to fill in the gaps in this picture once we have life detection from Mars, if there is life there. From the evidence so far, we might well find habitats on Mars without Earth life in it, habitats that Earth life could inhabit. There's another way also that Earth life might not be in those habitats. That is if they are very rare on Mars and form for a few centuries then go away. Maybe the Earth life just doesn't get there in time with a few spores spread in the dust storms before the habitat disappears again. That happens on Earth also in newly formed lava flows but it only takes a few weeks for Earth life to colonize them. On Mars maybe it takes centuries or millennia. It might be in some of the habitats and not in others. It might occupy them on Mars for some time, even perhaps occasionally for millions of years, then go extinct.

So anyway - Zubrin and a couple of exobiologists have put forward a thesis according to which they think that habitats on Mars will have exactly the same lifeforms that the sam habitats have on Earth. But they don't go into details about how it would happen. It's largely "hand waving" arguments, and it's by no means proven and is rather controversial. I think many exobiologists would be very surprised if that's what they found. And would be bound to be some differences which you'd want to explore and understand, if he was right, to learn which lifeforms got to Mars, how they got there, and how they survived when they got there, what was the first lifeform to get there, and how they evolved and changed after spending tens of millions of years, perhaps billions of years, in Mars conditions.

But could also be that it just never happened. Or that there's a mix of Earth and native Mars life that gets on fine on Mars but won't work any more after you introduce more Earth species. Or perhaps Zubrin is right and somehow all the Earth lifeforms that could survive in those habitats are already there. If so that would be an extraordinary event that you'd want to understand well before introducing more present day Earth life to Mars. Or there might be habitats but no life, as Charles Cockell talks about, and again you'd want to understand that well too. It could give us insights into exoplanets that don't have life, and into the role of life in geological processes on Earth as a "control" and tell us something about how far complex chemistry can get on its way to life on a planet without life.

One way or another, I think it is just far too soon to say that it is okay to introduce Earth life to Mars.

We'll only be able to fill in the gaps in this picture once we have life detection from Mars, if there is life there. We saw earlier that Zubrin and a couple of exobiologists have put forward a thesis according to which they think that habitats on Mars will have exactly the same lifeforms that the sam habitats have on Earth. If that is so, then there is nothing to worry about in either direction. But they don't go into details about how it would happen, and it is hugely controversial. If we find that life on Mars is identical to Earth life in all respects I think there would be astonishment about this. How did it get there? Why didn't it evolve differently from Earth life over the millions of years it has been there?

We'll only be able to fill in the gaps in this picture once we have life detection from Mars, if there is life there.

However, from the evidence so far, we might well find habitats on Mars without Earth life in it, habitats that Earth life could inhabit. There's another way also that Earth life might not be in those habitats. That is if they are very rare on Mars and form for a few centuries then go away. Maybe the Earth life just doesn't get there in time with a few spores spread in the dust storms before the habitat disappears again. That happens on Earth also in newly formed lava flows but it only takes a few weeks for Earth life to colonize them. On Mars maybe it takes centuries or millennia. It might be in some of the habitats and not in others. It might occupy them on Mars for some time, even perhaps occasionally for millions of years, then go extinct.

Zubrin and a couple of exobiologists have put forward a thesis according to which they think that habitats on Mars will have exactly the same lifeforms that the sam habitats have on Earth. But they don't go into details about how it would happen. It's largely "hand waving" arguments, and it's by no means proven and is rather controversial. I think many exobiologists would be very surprised if that's what they found. There would be bound to be some differences which you'd want to explore and understand, if he was right, to learn which lifeforms got to Mars, how they got there, and how they survived when they got there, what was the first lifeform to get there, and how they evolved and changed after spending tens of millions of years, perhaps billions of years, in Mars conditions.

One way or another, I think it is just far too soon to say that it is okay to introduce Earth life to Mars.

Planetary Protection, Legal Ambiguity, and the Decision Making Process for Mars Sample Return

There are many domestic and international regulations to be negotiated which weren't present at the time of Apollo, and many new laws to be passed. She identifies the National Environmental Policy Act (NEPA) as probably the most important legal hrudle - likely to need to formal environmental impact statement, and public hearings, which would take as long as several years to complete. It would be a process that would be carried out in an open fashion with public debate. In the past these environmentally related law suits have often lead to legal challenges and lengthy delays. And the courts would not toleate shortcuts. NASA would not be the only agency involved in these legal decisions. Others would include probably the Environmental Protection Agency, the Department of Agriculture, the Department of Health and human Services, and the Occupational Healhth and Safety Administration, as well as several others. Quarantine regulations are likely to be particularly tricky.

This then would be followed by Presidential Directive NSC - 25, which has to be carried out after the EIS is completed, involves multiple agencies again and ends with Presidentail approval to launch. It would also involve numerous treaties, conventions and international treaties. It can also potentially involve the domestic laws of nations that are not receiving the sample, because the potential effect of the worst case scenario could impact on all nations.

It's an area where I feel have some training and expertise, given that my postgraduate research was into topics in mathematical logic, though I didn't specialize particularly in Roger Penrose's ideas. I'm also a programmer too, author of : Bounce Metronome, Tune Smithy , Lissajous 3D, and Virtual Flower - so again though I don't have expertise in programming artificial intelligence, I do have some background in computing generally, as someone who has been programming on and off since the early 1970s.

We are safe from extinction from astronomical disasters for hundreds of millions of years into the future, long enough to evolve again from scratch from the smallest multicellular microscopic organisms. If we are still here half a billion years from now, when the oceans start to get too hot for habitability - then we must have a very stable civilization :). There are many things we could do at that point if we have technology just centuries ahead of where we are now, never mind hundreds of millions of years ahead.

(see for instance this paper)

<a href="https://youtu.be/7WorhUTyURg"><img src="Touch_Mars_videos/videoskim.jpg" width="560" height="315"><br> (click to watch on YouTube)</a>

As it is, as I dramatized in the future fake news story in Should we return samples from Mars right now? we risk the geologist returning their carefully selected samples, and handing them to the astrobiologists, who then throw up their hands and say "What am I supposed to do with this?"The astrobiologists have moved on so far in their ideas and instrument designs since Viking, but time after time they get descoped and nthey never get the chance to fly any of their instruments on Mars.

NASA's exploration program for Mars, and to some extent, ESA's also, is based on the priorities of planetary geologists, physicists, chemists, and space colonization advocates. They all are pushing in the same direction - to do global surveys of Mars, to study and learn the geology in great detail, the physics, the minerology,and the processes that shaped Mars. They have search for water, past and present, as a top priority. They think we should only start to look for life on Mars after we have understood it very thoroughly in terms of the physics and the geology. They often emphasize searches for fossils and microfossils. Any experiment to look for life directly in situ ends up way down in their list of priorities, passed over in favour of a wide variety of geological mapping experiments.

Most books and articles on this topic tend to put forwad the perspective of the physicists, geologists, and space colonization advocates, and these are also the views that have most influence on NASA's direction through the decadal surveys. They are all pushing in the same direction - to study and learn the geology in great detail, the physics, the minerology, the chemistry, and the processes that shaped Mars. To continue to "follow the water" to find more and more details about water on past Mars, as our top priority. They see the biological experiments on Viking as an example of how not to do it, and would only to start a serious search for life at a much later stage. They often focus on a search for fossils or microfossils. They also see a sample return as the best way to settle the astrobiological questions. If we send specialist life detection instruments to Mars, they would only do this at a much later date..

Meanwhile the astrobiologists forecast that NASA's extremely expensive multi billion dollar sample return program is likely to return samples that are as ambiguous for astrobiology as the controversial Mars meteorites we have already. They are pretty much unanimous on this, and say that we don't know enough yet to intelligently select a sample to return based on its geology. Any organics in the samples would probably come from meteorites and comets originally, and would be as problematical to interpret as the organics in the Mars meteorites. They have designed many in situ life detection experiments that overcome the issues with the unusual chemistry on Mars that afflicted the Viking landers.Their priority is now, and has been for many years, to send these to Mars at the earliest opportunity.They don't see a search for fossils as a top priority, as they have learnt from their experience of studies of Mars meteorites and samples from Early Earth that alleged microfossils can be controversial and difficult to interpret.

So my view here is that I think we need a change of direction. I think it is time to follow the recommendations of the astrobiologists, send their in situ instruments to Mars, and see where this leads. So, expect strongly expressed views here. Hopefully it is clear when I'm presenting my own views and ideas and when I'm describing the views and ideas of others.

You may be surprised, perhaps even shocked, at how their ideas about how to search for life on Mars differ from the views of the geologists, physicists, chemists and space advocates, and from NASA's road map. Their focus is on in situ searches on Mars, and they think that the expensive sample return mission is likely to return ambiguous samples

I will argue that it's time for a change of direction. I think we should follow the ideas of astrobiologists about how to look for life on Mars, and see where it leads.

.They think that NASA's very expensive multibillion dollar program to return a sample from Mars is likely to do little more than add a few more samples like the "Mars meteorites" we have already. These have organics in them - but this proves nothing as Mars will have large amounts of organics from meteorites or comets or abiotic processes on Mars. For this reason, they don't think we know enough to intelligently select a sample to return based only on geology and detection of organics. Such samples are likely to be difficult to interpret, controversial, and prove nothing.

But the astrobiologists see tings very differently. They agree that all that is of great value, they are not saying to stop doing this geological study. But they see as the top priority for their own discipline, to send highly capable life detection and biosignature detection instruments to Mars right away. They don't see microfossils as likely to settle questions either unless very obvious, again based on their experiences of analysis of meteorites, also of analysis of ancient deposits on Earth with controversial microfossils in them. For them, it's all about the search for unambiguous biosignatures, for past life. For present day life, the search for microbes that can metabolize and be detected engaged in living processes. They are also very aware that you can have geologically similar formations, some with life, and some without. For instance in the Atacama desert, some of the gypsum pillars are lifeless, and some have life, depending mainly on the relative humidity of the location as it varies over the year. If you were to just return a gypsum pillar sample from the Atacama desert, without detecting life first, it's likely to be lifeless. Organics also don't mean life on Mars, because of the meteorite and comet impacts and other non biological ways of creating organics. They also see the search for nitrogen based organics and nitrates as a top priority too, after the search for water, something that NASA hasn't yet taken on board. That's because nitrogen is probably essential for life, and rare on Mars.

For all we know, then it might be that Viking did discover life in the 1970s. If it did, then rather embarrasingly for NASA, the very first mission to send a modern updated set of astrobiological instruments to Mars may find it. And if not, well they think that Viking was on the right linese. The Viking biological instruments naturally enough were not designed to cope with the unexpected chemistry of the Mars surface. But that's a solvable problem. Immediately after Viking, biologists designed new instruments which we could send there, which addressed these issues. But though geologists and physicists have been able to move on and to send increasingly sophisticated instruments to Mars and elsewhere, improving the designs as a result of earlier experiments with null results, the exobiologists have not been able to send anything to Mars or anywhere else in our solar system, not since Viking. How can we detect life if we don't try to look for it? Also, almost unanimously, they are agreed that the next step for astrobiology is to search in situ, not to do a sample return, at least, not yet. Chris McKay is the only significant exception here. He thinks it could be worth sending a low cost mission to just land on Mars anywhere, grab a sample of dust and atmosphere, and return it for analysis, but he also doesn't see any virtue in an elaborate mission to cache samples to return based only on a geological study. Yet it seems that these views just haven't been heard by the rest of the planetary science community, or if heard, ignored, and not acted on.

The main differences are

Astrobiologists want to send life detection instruments to Mars right away. They see no reason to wait for results of geological surveys
They don't think we can select samples for study on the basis of geology. They also generally don't see searches for fossils or microfossils as our top priority - because such structures are likely to be ambiguous, as we found with ALH84001 and many controversial microfossils from early Earth. It's interesting but not our main focus.
They think the "follow the water" has already yielded enough results so that we should move on to "follow the nitrogen" which is in short supply on Mars and essential for life - and for direct life detection
They know how to address the issues of the surface chemistry that confused the Viking instruments. They want to send updated biological instruments to Mars at te earliest opportunity.
They don't see any great value in returning a sample from Mars at this stage. They predict that a sample selected on the bass of the geology and presence of organics is likely to be as ambiguous for the search for life on Mars as the Mars meteorites we already have. The one exception here is Chris McKay who thinks there may be value in a low cost mission to just grab a sample of the dust and air from anywhere on Mars and return that, but he also can't see the value in a high cost mission to select samples based on geology to return to Earth.

Maybe past life is so hard to distinguished and degraded that we will never be able to tell if it ever had past life

What if there is nothing we can do about it, that we've contaminated Mars already, and we just have to resign ourselves to endless discussion about whether Mars had present day life before the first spacecraft arrived there from Earth?

Deep underground
In caves
Past life that goes extinct
Life that flourishes every few million years - this is quite possible on Mars with its large swings in habitability. It's like the way poppies and other flowers bloom in a desert after the first rain for years, but on a longer timescale.
Sparse populations on the surface right now.

The last of these is the newest. Life in microhabitats similar to those in the McMurdo dry valleys could be hidden from these atmospheric measurements simply because of low populations, and a slow metabolism. For details, see "How much oxygen would surface photosynthetic life produce on Mars? " below.

For that matter, let's indulge in a little speculation again - what if Earth already had life before the impact of Theia - or if Theia had life, according to that impact hypothesis for formation of the Moon? Perhaps the fragments from that impact might have reseeded Earth as well as seeding Mars with life, maybe early Venus too.

of example in this test of three of the Apollo era spacesuits, two of them leaked more than 3000 ccs per minute, and the best one leaked 700 ccs per minute (see page 35).

"As the Mars environment may also harbour current or past life, it is also a consideration that a Mars EMU provide some measure of quarantine against human/bacterial contamination of the surface (and indeed vice-versa). The high volume of oxygen and required flow rates in gas-pressurised suits leads to a high leakage rate: it is predicted that over 50 litres of human borne bacteria and other airborne effluent would escape through suit bearings and joints during each EVA, potentially contaminating soil, fossil and atmospheric samples [13]. Perhaps more critically, this leakage represents a sizable wastage in oxygen supplies. A solution may be to pressurise the body with the Martian atmosphere, leaving only the head pressurised with oxygen."

Pumice and ash floating on Lake Nahuel Huapi, Bariloche, Argentina

We have only limited ground data on the ages of the lunar craters, from Apollo, as they sampled only a small part of its surface, most of it affected by the debris from Mare Imbrium. So most of the early cratering history timetable for the Moon is largely guess work. According to some recent research, such as this paper, the very largest impacts on the Moon may even all date back to as long ago as 4.35 billion years ago or earlier, soon after the formation of the Moon. They think there were no ocean boiling and Earth sterilizing impacts after that. But there could have been large impacts that covered large areas with melts. See this paper.

After all we are used to a planet with just one intelligent species on it.But a few tens of thousands of years ago, then we had several distinct species of hominids (though able to interbreed). In the future, we may have many

Such large impacts would probably also melt and sterilize Earth's entire surface to some depth and boil away its oceans. So we are talking about very early stages in the evolution of life here. The very process that sends life to Mars probably leaves a sterile Earth behind, or at least sterilized to considerable depths. Perhaps Earth also gets reseeded by life from the impact itself. In that way the life on both planets could be related, and both could be seeded from an earlier Earth, but the conditions that lead to this would be very violent.

To fight against double the delta v requires more fuel by the rocket equation (fuel has to carry more fuel).
F, and when you take account of the need to discard the ascent stage, the payload fraction ends up being very small for an ascent from Mars. For instance in this paper looking at possibilities for a Mars sample return, a single stage rocket would need 300 kg to send 15 kg into orbit, if the first stage is 79% propellant. Meanwhile a rocket to send a sample all the way back to the Earth from the Moon can send a 75 kg payload back with a lunar launch mass of 500 kg with only 71% of the first stage consisting of fuel. That's a difference between less than a 7 to 1 ratio for the Moon, and a 20 to 1 payload ratio, and it doesn't take account of the extra delta v needed to get the Mars sample from Mars orbit back to Earth. The optimum in terms of mass is a two stage rocket taking off from Mars, which would have a total of 110 kg, to send 15 kg into orbit around Mars. That's adding to the complexity however

Safety - Moon is far safer than Mars as we can get back in two days and we can have "lifeboats" sufficient for the entire crew kept permanently supplied with all they need to get back to Earth.
Economics - the only viable exports from Mars known at present are intellectual property - I find it deeply unconvincing that a Mars colony could pay for its hundreds of millions of dollars per person habitats and millions of dollars for a two dozen EVA spacesuit through IP. I expect the trade in IP to be mainly the other way from Earth to Mars. There are many suggested revenue streams for the Moon including material exports, tourism, adventure etc.
The near 24 hour day on Mars seems an advantage, as it is the same length as Earth's day (approximately) but that's where the resemblance begins and ends. The dust storms block out the light for weeks on end and it makes the nights extremely cold, cold enough for dry ice to form even in the tropics for many days of the year, and also huge swings in temperature which are an engineering issue both for life support and materials used for construction. The polar regions of the Moon especially have sunlight nearly 24/7 and near constant temperatures
Dust is hazardous in both places for different reasons, but is easier to deal with on the Moon and we also know from direct experience that humans can cope with some level of exposure to lunar dust. Mars has rounder grains, but it has perchlorates and probably chlorates and chlorites and those latter especially have major health issues. Also the Mars dust storms mean you can never have an area around a base permanently cleared of dust as you could do on the Moon where you have only electrostatic levitation of the dust to deal with.
Greenhouse construction is similar. The CO₂ atmosphere of Mars is not an advantage for agriculture as CO₂ is a waste gas that will build up constantly, if you import more food than you can grow and is only needed in trace amounts of a few kilograms for the entire habitat. Anyway the Moon has carbon dioxide in the form of dry ice at its poles. It also has ammonia as a source of nitrogen.
The Moon has ready made lava tube caves. Mars does also. But the lunar caves are likely to be far larger in its lower gravity.
Landing on Mars is by far the most hazardous landing in the inner solar system and we don't have the technology yet to land humans. Elon Musk thinks that supersonic retropropulsion will do it -if it does it is an extremely dangerous approach involving a rocket that has to skim close to the surface, to decelerate, so close that it would have to pass inside the Valles Marineres if landing in that region of Mars, and then has to land vertically like his first stages. He is many technological steps away from even proving it is possible, never mind safe. Returning humans from Mars once you have landed there is another huge challenge. We have yet to return even robotic vehicle.

We could land on the Moon with 1960s technology and return to Earth. We don't have the technology to do that either right now, but in the case of the Moon, we do know how to do it, in great detail. It is more a matter of reinventing modern technological methods for a known problem with proven solutions.
Pinpoint landings on the Moon. With no atmosphere, and with modern technology, we can do pinpoint landings while at present on Mars we need a landing ellipse and a landing spacecraft has to be able to land safely anywhere within a region of hundreds of square kilometers - either it has to be very flat, or the spacecraft has to have a way to avoid obstacles like boulders and cliffs through Artificial Intelligence during the last few seconds of the landing.

There is no way a human could react quickly enough to make those decisions. Neil Armstrong couldn't have guided a spaceship to a safe landing on Mars. Elon Musk has demonstrated pinpoint landings of a first stage on a barge. He has not yet demonstrated pinpoint landings from orbit, and he is a long way from proving he can achieve a pinpoint landing on a selected spot on Mars. Using present day technology his "colonists" could easily land many kilometers away from the habitat they are aiming for.
On Mars, the habitats themselves would be a landing hazard until we have total confidence in pinpoint landings on Mars. They would need to have a landing ellipse that doesn't include the habitats, which with present day or near future technology would mean a journey of kilometers to get to the habitats from the landing site - or else running a risk of landing right on top of them by mistake, with the rocket falling over or destroying the habitat. Would you like to be on Mars watching a rocket land and knowing that there was a chance of it hitting your habitat? I'm sure they could solve this issue eventually, but it just isn't an issue at all for the Moon, with its absence of an atmosphere.
The higher gravity of Mars, a third rather than a sixth of Earth, may or may not be an advantage. We have no idea. It could even be that lunar gravity has an advantage. On the Moon then if we do need to have horizontal centrifuges for gravity for health, then the spin motions may be better tolerated due to weaker gravity along the spin axis and the construction perhaps somewhat simpler.
The vacuum of the Moon is an advantage, it permits high grade manufacture of electronics indeed it is better than Earth - it could permit methods that are uneconomic on Earth due to the high costs of maintaining a vacuum as hard as the lunar vacuum. Mars just has a "laboratory vacuum" for its "atmosphere". It's of no use for vacuum deposition and manufacture of electronics.
The Moon has nanophase iron in its dust which means you can easily microwave it to make glass, takes the same amount of microwave energy as you need to boil the same mass of water. All the iron in the Mars dust has rusted, as you can tell from its colour. It has a few iron meteorites on its surface, and that is it by way of pure iron as far as we know.
The Moon has double the sunlight of Mars making solar power easier
The Moon has 14 Earth day nights, so that's a disadvantage
However the Moon at its poles has sunlight 24/7, and what's more, unlike Antarctica, this is year round apart from a day or two in the entire year when the sun is briefly hidden behind local topography - due to its axis aligned nearly perpendicularly to the ecliptic - if you go to the right places

Here are a few more.

Planetary protection of course - that's what this book is about. The risks making native Mars life extinct if it exists, or confusing its study especially after a crash of a human spaceship on Mars with its global dust storms. The Moon doesn't have this issue.
On Mars, the habitats themselves would be a landing hazard until we have total confidence in pinpoint landings on Mars. They would need to have a landing ellipse that doesn't include the habitats, which with present day or near future technology would mean a journey of kilometers to get to the habitats from the landing site - or else running a risk of landing right on top of them by mistake, with the rocket falling over or destroying the habitat. Would you like to be on Mars watching a rocket land and knowing that there was a chance of it hitting your habitat? I'm sure they could solve this issue eventually, but it just isn't an issue at all for the Moon, with its absence of an atmosphere, making pinpoint landings easy
Because there is no aerobraking, you can abort the landing on the Moon at any time. It also happens slowly enough for humans to take over control if necessary, like Neil Armstrong navigating to a safer landing site. A landing on Mars has to be automated, with many decisions being made rapidly on timescales of seconds. There would be nothing a future Neil Armstrong could do in time, if the landing went wrong on Mars.
The lunar night is 14 Earth days long, so that's a disadvantage. However, it doesn't have the Martian dust storms, which can sometimes block out nearly all the sunlight for weeks on end. So you'd need roughly the same amount of backup battery power in both places. Except at the lunar poles where you have sunlight 24/7 nearly year round.
The near 24 hour day on Mars seems an advantage, as it is the same length as Earth's day (approximately) but that's where the resemblance begins and ends. The nights are extremely cold, cold enough for dry ice to form even in the tropics for 100 days of the two Earth years long Martian year, yet above zero in daytime, so with huge swings in temperature which are an engineering issue both for life support and materials used for construction.
Dust is hazardous in both places for different reasons, but is easier to deal with on the Moon and we also know from direct experience that humans can cope with some level of exposure to lunar dust. Mars has rounder grains, but it has perchlorates and probably chlorates and chlorites and those latter especially have major health issues. Also the Mars dust storms mean you can never have an area around a base permanently cleared of dust as you could do on the Moon where you have only electrostatic levitation of the dust to deal with.
We have no idea what level of gravity humans need for health so you can’t say that is an advantage of Mars, at least not at present. The higher gravity on Mars, a third rather than a sixth of Earth's, may or may not be an advantage. It might also depend on the person, age, sex etc. For all we know, lunar gravity could be better for health than full g. We just don’t know yet. Or we might need artificial gravity to stay healthy on both the Moon and Mars.
Low lunar gravity makes construction simpler, and would permit human flight with flapping wings as a recreation If we do need to have horizontal centrifuges for gravity for health, then the spin motions may be better tolerated on the Moon, due to weaker gravity along the spin axis and the construction perhaps somewhat simpler.
Greenhouse construction is similar. The CO₂ atmosphere of Mars is not an advantage for agriculture as CO₂ is a waste gas that will build up constantly, if you import more food than you can grow and is only needed in trace amounts of a few kilograms for the entire habitat. Anyway the Moon has carbon dioxide in the form of dry ice at its poles. It also has ammonia as a source of nitrogen.
The Moon has much of scientific interest and many resources that we didn't know about in the 1960s. There are many books describing in detail how those resources could be used.

, but Mars transfer requires a delta v 3.4 km/sec from LEO, similar to the delta v of LEO to translunar orbit of 3.02 km / sec

Using an ultrasound machine on the ISS, experimenters found that the heart is 9.4% more spherical in space.

Need to send robotic explorers like VAMP to the Venus clouds first

The idea of colonizing Venus clouds of course depends on the clouds not having some form of life there that is hazardous to humans, or that would be hazardous to Earth if brought back here. Venus seems a perfect place to send humans to explore, but let's explore it with sterile robots first, if there is any chance of finding life in the atmosphere, even if we think the chance seems rather remote. We can learn what we need using robots. Then if there is life there, we can find out whether it can survive on Earth or vice versa, and whether there is any hazard from it at all, and whether Earth life can impact on it, before we decide whether to send the first humans to the Venus clouds.

Perhaps the chance of life in the Venus clouds is low, but on the other hand the evidence is rather intriguing when you look at all of it in detail - the evidence of non spherical particles, the out of balance chemistry that on Earth would signify life, the dark in the UV could be photosynthesis or protection of life using pigments, etc.

It could be an issue for forward contamination from Earth too. If there is life there already, perhaps it might create microhabitats in the clouds in some way. If Venus even evolved macroscopic floating life using hydrogen for buoyancy then those lifeforms themselves could be a potential habitat for Earth life - and they might well have no defences at all against our form of life. And anyway, life modifies its environment so if there is life there already, it might create conditions in some way habitable for Earth microbes. If so the clouds may be more habitable than they seem from a distance. We do have acidophiles already that can tolerate levels of acid nearly as extreme as the ones in the Venus clouds already.

We might also be able to prove that it is a problem, but in one direction only, e.g. that Earth life is harmful to Venus life but not in the other direction - or vice versa, e.g. if one of the lifeforms is far more highly evolved in some sense than the other. Or just because the conditions are so different, maybe Earth life can't survive on Venus, or maybe Venus life can't survive on Earth, and maybe both of those things are true. We just can't figure that out in advance. We can only find out these things by studying it.

So, we don't know if there is life there. If there is, we don't know if it is a problem for sending humans to the Venus upper atmosphere. For these reasons, I don't think we should launch a HAVOC style human mission to the Venus clouds right away, not without robotic precursors. But we have lots of in situ ways to study and detect life and if there is life there we can find it. So we can do lots of VAMP style robotic missions there. If we are confident early on that there's no life in the clouds, we then can send humans as soon as it is technically feasible. If we do find life there, or evidence that it might be there, we can study it in situ first, to find out if it is hazardous for us in any way or if Earth life is hazardous for it, then decide what to do next based on our findings.

Limitations of the method

It is not enough to rule out life in the sample. For example, it might find the culture we provide so alien to it, that it can't metabolize at all, or it might even be killed by it. Life that has hydrogen peroxide and perchlorates inside the cell would probably "self destruct" if warmed up and introduced into a medium of liquid water with nutrients. See Life that uses hydrogen peroxide, or perchlorates, or both, INSIDE the cells (below). And of course the chiral labeled release also depends on it exhaling a gas that contains the carbon such as carbon dioxide, or methane, but most forms of Earth microbe do this.

However, i f there is ife there, and it resembles Earth life, it may well exhale carbon in some gasous form when it metabolises organics. In preliminary tests before the mission, the experiment detected life in all the samples from Earth except for a few samples from Antarctica. So, if there is any life like that and it starts to metabolize and is not killed by the culture medium, then Viking's labeled release would detect it.

It is not enough to rule out life in the sample, as it is also possible that some forms of Mars life can't even metabolize in a culture medium if we provide it with warmth and liquid. It might be so slow to "wake up" that it does nothing for the duration of the experiment. Or it might find the culture we provide so alien to it, that it can't metabolize at all, or it might even be killed by it. By way of example, life that has hydrogen peroxide and perchlorates inside the cell would probably "self destruct" if warmed up and introduced into a medium of liquid water with nutrients. See Life that uses hydrogen peroxide, or perchlorates, or both, INSIDE the cells (below). And of course the chiral labeled release also depends on it exhaling carbon dioxide, methane, or some gas that contains the carbon.

It is not enough to rule out life in the sample, as it is also possible that

Mars life might be so slow to "wake up" that it does nothing for the duration of the experiment.
It might find the culture we provide so alien to it, that it can't metabolize at all
It might even be killed by it. By way of example, life that has hydrogen peroxide and perchlorates inside the cell would probably "self destruct" if warmed up and introduced into a medium of liquid water with nutrients. See Life that uses hydrogen peroxide, or perchlorates, or both, INSIDE the cells (below).
The experiments depends on the life exhaling carbon dioxide, methane, or some gas that contains the carbon. For instance life that exhales hydrogen sulfide or sulfur dioxide would not be detected

However if there is ife there, and it resembles Earth life, it may well exhale carbon in some gasous form when it metabolises organics. If there is any life like that and it starts to metabolize and is not killed by the culture medium, then Viking's labeled release would detect it.

Same image colour adjusted with red at 80% (255 adjusted to 204) and green and blue at 60% (255 adjusted to 153). Brightly coloured purple life like this would be noticeable on Mars but not so obvious as on Earth.

Here, I haven't yet found a paper that discusses the likely colour of Mars photosynthetic life, life on exoplanets yes, but not on Mars. However, it seems an interesting and fun topic. So this section consists of a few ideas and suggestions to help get us started. As usual do say if you know of anything on this topic.

These figures will vary depending on the time of year (optical depth of Spirit drops to 0.2 mid winter when the atmosphere is at its clearest), and of course, in the other direction, much of the light is filtered out during dust storms. An atmosphere is optically thick, if the optical depth is greater than 1, meaning that on average a photon can't pass through it without being absorbed.

Impacts into comets would surely create liquid water temporarily, but it would freeze solid and never escape into space.

Ideally you want to see smaller structures than that, the structure of protocells if they exist, and other sub-optical limit structures, so I do wonder also about optical microscopes that go beyond the diffraction limit, but I'd have thought they are probably too complex to send into space?

So studying the old Apollo sites for microbial contamination could help give us our first ground truth for planetary protection for future explorations by humans, also we can study the contamination introduced by our new human and robotic explorers there. "Future robotic and human missions to the Moon could provide a unique opportunity to carry out ground-truth experiments using in situ life detection instruments to help understand the extent of forward contamination by robotic spacecraft and human presence over a limited range of conditions and time"

The organic contamination would be limited to a small region around the base. The electrostatic transport would move a few microbial spores further away from the base, yes, but in quantities so small they wouldn't impact on the science ,given that there is nowhere for them to replicate. There are currently no regulations at all on missions to the Moon, including missions with humans, except to document what you do. There may be regulations in the future, but it's hard to know what they would be yet. The main ones might be - a regulation to use more volatile rocket fuel so as not to create lasting lunar atmospheres with high molecular weight fuels, and some kind of "lunar parks" approach where e.g. historical sites such as Apollo 11 landing site get some protection. I can imagine that perhaps if there are small localized sites of special scientific interest, there might be rules there too. In Antarctica then researchers in the McMurdo dry valleys use a corral system to keep microbes limited to their camp, staying within a small area of perhaps 50 square meters for the duration of the week long visit.

I imagine perhaps they might have regulations like that for studying the lunar ice if it became an issue of people walking over it introducign confusing organics?

We can also bring life to the Moon to do long term experiments there, including tests to see how the life evolves in space conditions of cosmic radiation and low gravity. We can do tests of lunar greenhouses in the conditions there, find out what pressure levels they need (lower pressure being technically easier to do).

Could the ice at the poles be habitable? Well the thing is that it is not exposed to sunlight so there is nothing to warm it up enough to be liquid. It's possible on Ceres because it has a thick icy crust and meteorite impacts expose that ice to the surface- it has ice in Oxo crater exposed to direct sunlight which must be rapidly subliming (see Search for early life on Ceres).

The ice at the lunar poles would of course melt locally after meteorite impacts, must frequently get small amounts of liquid water forming after small impacts, but this would soon freeze over. Liquid water could be prevented from evaporating by a layer of organics, not too implausible for comet originated ice - but to have the thermal insulation to form long lived impact lakes the ice would have to be deep and it's probably only meters deep.

there are permanently shaded regions up to 58 degrees from the poles (only 32 degrees from the equator). Though these regions are too warm to have ice on the surface, there may be ice there underground. See Ice may lurk in shadows beyond Moon's poles (Nature, 2012). If it had any ice heated geothermally at some depth, or on the surface, warmed by sunlight, then theoretically, it could remain liquid if it had an impermeable covering layer of organics or other materials.

https://workspace.imperial.ac.uk/opticalandsemidev/Public/Publications/Life%20Sciences%20Investigations.pdf

During the era of Apollo, in the 1960s and 1970s, the field of dust toxicology was in its infancy and samples of lunar dust were not examined for toxicological effects. The focus was instead on the potential risks due to microbes.

It has been identified that lunar dust contains several types of reactive dust. Of these many are in the respirable range, defined previously as those particles with diameters \3.5 lm (Liu et al. 2008) although \10 lm is considered by other authors

Small dust particles may be hazardous to human health if they were to enter the lungs, particularly if exposure were for a prolonged period of time, as might be the case for future lunar missions. Impact glass may be easily dissolved in bodily fluids, releasing the np-Fe0 grains, which are very reactive, owing to their redox potential and relatively large surface area per unit mass. In addition the surfaces of particles are unlike any terrestrial analogue and are likely to be highly reactive on account of radicals generated in the highly reducing lunar environment, in which there is no mode for passivation. The extent of this reactivity is key to the toxicity but is not known. Various attempts to reactivate lunar dust and analogues by fracturing and radiation exposure have been attempted but there is no means of verifying the results in the absence of in situ measurements or access to pristine, unpassivated lunar dust. The rate of passivation for particles upon contact with a humid atmosphere like that of a human habitat is not known but may be of the order of a day.

The study Planning Considerations Related to the Organic Contamination of Martian Samples and Implications for the Mars 2020 Rover (available to download as open access from MIT) discusses it in detail.

So, I suppose it is not impossible theoretically, to have liquid water on the Moon, Carl Sagan hypothesized this before the lunar landings. And indeed it must have short lived liquid water occasionally in small quantities after impacts into the ice deposits. But so far, nobody is hypothesizing life or habitats for life there.

Ceres does have ice in sunlight on its surface, exposed to sunlight, in Oxo crater which must be rapidly subliming (see Search for early life on Ceres). But the Moon doesn't have any ice in sunlight as far as we know. It's possible on Ceres because it has a thick icy crust and meteorite impacts expose that ice to the surface. The ice could be melted by impacts. There's some indirect evidence from comet Wild of impact melting in comets which could create a temporary habitat. .Life or prebiotic chemistry in comets

Also the Moon doesn't have global dust storms. It does have electrostatically levitated dust, which surprisingly can levitate even particles 140 microns in diameter, and the finer dust goes so high that the Apollo astronauts sketched rays of sunlight hitting the dust at sunrise and sunset from orbit. A microbe in a 140 nm particle would be protected from UV (though of course affected by the electrostatic discharges that levitate the particles in the first place).

Chris McKay with his "lego principle" suggests a general way of looking for it, which makes no assumption that it resembles Earth life. His idea is that extraterrestrial life would favour some molecules over others in a way that would be very noticeable.

The idea here is that abiotic processes produce smooth distributions of molecules, shown schematically here as a curve. Molecules that are chemically similar have similar concentrations generally.

While biotic processes tend to focus on particular molecules out of the many possibilities, shown schematically here as vertical lines. E.g. Earth life all uses a particular set of 20 amino acids to build proteins. It also uses only one of two mirror image forms of asymmetrical molecules. So - extra terrestrial life he thinks would be likely to be similar, it would select particular molecules out of the many available and we'd see a large bias towards those ones, while others that are chemically similar and which you'd expect to be produced in equal numbers would be much rarer or not there at all.

See his What Is Life—and How Do We Search for It in Other Worlds?

See Strengths and weaknesses of the "lego principle" approach (above)

This could be a distinctive pattern even if the life doesn't use any of the familiar biomolecules. The signal however would be degraded if the organics are altered, through heat, ionizing radiation, chemical reactions etc. It also might be hard to distinguish this signal in a sample that's a mix of life with abiotic organics.

The paper about their concept is here, but it's behind a paywall. However there are many details also here.

Bill Nye, CEO of the planetary society, saying we should send humans to Mars by 2023, and to land by 2025. I think there is much to admire in the work of the Planetary society. But on this particular point, I am unable to give them enthusiastic support.

I don't know how long it would take to do a reasonable first attempt at a biological survey of Mars from orbit, and to have a decent first idea of what Earth microbes could do on the surface. Maybe not that long, if we had the resources typically given to human missions to do it from orbit. But however long it would take, surely it can't all be done in a single mission within a two year timeframe? It's bound to turn up questions, things we don't understand that need follow up missions and probably new hardware on Mars.

They would kill all the blue whales probably within a few years, many other species would be extinct, and environments devastated. They would use chemical, biological and nuclear warfare and torture. They'd destroy each other with carpet bombing. We've learnt to cope with all this technology and developed ways of working with it and modifying our behaviour, at least to some extent. We still have many issues, but compared to what the issues would be for people used to nineteenth century ways of thinking suddenly given our technology, with no time to adapt to it socially,..

the ExoMars Trace Gas Orbiter

See also Paul Spudis' Delusions of a Mars Colonist

Steven Lyle Jordan's Space is not a frontier

You could say that Carl Sagan's planned "biological exploration phase " started and then stopped immediately with the two Viking spacecraft. We have done no direct life detection tests on Mars since then. ExoMars in 2020 will probably be the first mission to be able to search for present day life in situ on Mars to some extent, and still is not as sensitive for this task as Viking was designed to be (with controversy of course about whether it discovered anything because of the unusual Mars chemistry). And even with ExoMars, its main focus is past life, with its search for present day life as a bonus. The area it's going to is not high on the list of candidates for present day life.

Phil Christensen was quoted by New Scientist as saying:

“If I was going to search for life on Mars I would certainly include landing and looking at some of these potential snow deposits,”

Pristine Mars

I fully understand how those who are keen on colonization of space want to land humans on Mars as soon as possible. They may be so keen on this that they think that it is far more important than any discovery in biology. But we aren’t talking about preserving some obscure microbe only of interest to microbiologists. What we discover there could lead to the biggest discoveries in biology of this century. It could be as big a discovery as the discovery of evolution or the spiral structure of DNA.

It’s only because introducing life to Mars is irreversible that we are in this situation. Their keenness to colonize Mars doesn’t give Elon Musk or Robert Zubrin or anyone else the right to make an irreversible decision about Mars for the rest of humanity. We are in it together and we all have a right to a say in this decision. The situation is particularly acute because there is a significant risk of a crash of the first human missions to Mars if we do send humans to the surface. See Why do spacecraft crash so easily on Mars? (above). A crash of a human occupied ship would be the end of planetary protection of Mars for science.

So, with this background - let’s keep Mars pristine for scientific study at least until we know what is there. Otherwise we may mess it up for future transformation, if we do try to change it, and we may also spoil the opportunity to make the next big discoveries in exobiology. It may be the equivalent of an exoplanet on our own doorstep in terms of the discoveries we could make there. So let’s keep it like that, not try to make it into a pale shadow of Earth before we know what’s there. Let's focus on other places to export our Earth's biosphere for now.

Pristine Mars

The main ones are (these links take you to the online booklet)

Why Mars Surface Life May Leave No Traces In Its Atmosphere: Our Rovers May Need To Go Up Close To See It

also my Our Spacecraft Could Look Straight At an Extraterrestrial Microbe - And Not See a Thing!

I did a survey of the scientific literature, to see what there is by way of proposed habitats and to investigate the range of views on the topic:

Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,... (long detailed survey article with many cites)

It's also available as a kindle booklet, and also online here with table of contents

If we think we will eventually introduce Earth life to Mars, we can test this first in Mars simulation habitats, perhaps on the Moon or in free space, huge ones, for far far less cost than for an attempt at terraforming Mars. We'll be able to complete the experiments in decades rather than thousands of years.

In the section Prestige or dishonour, first footsteps on Mars (below) I've dramatized this with a series of fake newspaper stories in a (hopefully) "alternative future" in which humans accidentally introduce Earth life to Mars, then regret what they did.

"Some leakage of spacesuit pressure is normal. The maximum allowable rate of leakage of the Shuttle EMU is 1.38 kilopascals per minute, and this is checked before the suit is brought back down to air lock pressure." The Space Shuttle Extravehicular Mobility Unit (EMU)

"EVA suits are proven to be inherently leaky; at least 50 leakage pathways have been identified aside from the porosity of suit materials themselves. Forward and back contamination is foreseen as inevitable. The analogous approach of sealing electronic boxes with HEPA filters (an approach used for robotic missions) is not tenable for humans. " Life Support and Habitation and Planetary Protection Workshop, 2006

"The minimum oxygen requirement during the 30-minute EVA emergency is estimated to be 0.092 lb/crewman, including the metabolic consumption and an allowance for the system and spacesuit leakage rate of 100 sccm." A Lightweight EVA Emergency System

The high volume of oxygen and required flow rates in gas-pressurised suits leads to a high leakage rate: it is predicted that over 50 litres of human borne bacteria and other airborne effluent would escape through suit bearings and joints during each EVA, potentially contaminating soil, fossil and atmospheric samples. Perhaps more critically, this leakage represents a sizable wastage in oxygen supplies. A solution may be to pressurise the body with the Martian atmosphere, leaving only the head pressurised with oxygen.

http://old.marssociety.org.au/amec2002/proceedings/17-James_Waldie_MCP_full_paper.htm#reference13

For example the NASA requirements for the Extravehicular Mobility Unit on the ISS is a maxumum of a tenth of a litre (100 cc) per minute (page 2 of this paper). In an eight hour EVA an astronaut could lose up to 48 litres of air. But the spacesuits also use an open system venting carbon dioxide and oxygen. One of their knowledge gaps for humans on the surface of Mars is how much microbial contamination this would lead to.

The amount of leakage can be reduced but it's not yet practical to prevent it altogether. With robots we can enclose any parts that can't be sterilized with HEPA filters to keep microbes within. But that's not practical for humans. For instance, if the spacesuit leaks 0.1 litres a minute, it would leak 48 litres of air complete with any microbes in it, in an eight hour EVA.

fter all it's not as if we need Mars as a place to introduce Earth life to in our solar system. There are many other places we can introduce Earth life to, to see what happens, with no impact on science at all, if we start by doing some work to make those places habitable to Earth life first. Lunar caves are a great example there. There are many of them, and they are probably huge. Give a section of a lunar cave some atmosphere, and some light and many plants can grow there as I cover in my An astronaut gardener on the Moon - summits of sunlight and vast lunar caves in low gravity in Why Humans on Mars First are Bad for Science. .

Another way to introduce Earth life off planet is to make habitats with artificial gravity from the materials in the asteroid belt, as I cover in Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths.

Also we can just work on making Earth more habitable, which could support many times its current population if we used the technology suggested for habitats in space, for instance with floating sea cities, or habitats in deserts, self enclosed like a space colony so having minimal impact on the rest of the Earth, even, for instance, bringing water to deserts that have recently been denuded by human activities.

So, why do this on Mars? Especially, why do it so quickly? Mars "as is" is of great scientific interest as a planet that used to be as habitable as Earth. Even if it doesn't have life and never had life - it gives us a precious opportunity to study an Earth like planet of that sort. The nearest other planet like that is light years away and we can't even send a robotic lander to it yet.

It's Rosetta tweets had 517,000 followers and the Philae lander tweets, 440,000.

This shows the amount of light transmitted through the atmosphere for global sunlight from 400 nm to 1000 nm as measured using photographs of the Mars Exploration Rovers calibration target (compared with its pre-flight callibrated reflectance). This was at a time when the sky was reasonably clear of dust, optical depth about 0.94 for Opportunity and 0.93 for Spirit. These figures will vary depending on the time of year (optical depth of Spirit drops to 0.2 mid winter), and of course much of the light is filtered out during dust storms.

SUrface Dust Mass Analyzer (SUDA) selected for Europa mission

Enceladus Lander for Mobile Observation - hopper for Enceladus exploration on the ground.

Enceladus Life Finder

h as Jupiter's ionizing radiation or cosmic radiation after the mission, before it can contact any potential habitat.

People had speculated that the nutrient-poor environment beneath Antarctica’s large ice shelves would resemble another underfed habitat—the world’s vast, abyssal sea floors sitting below 3,000 meters. But important differences are already emerging: The muddy floors of the oceanic abyss are populated by worms and other animals that feed on bits of rotting detritus that rain down from above. But the mud cores brought up so far from the Whillans grounding zone haven’t revealed such animals. Nor did Deep-SCINI’s cameras. “We saw no established epi-benthic community,” Powell says. “Everything living there can move.”

These new results are still extremely preliminary but a similar pattern was seen in the late 1970s when a hole was briefly melted through another part of the Ross Ice Shelf not as far inland—the so-called J9 borehole, which reached a layer of sea water 240 meters thick, sitting 430 kilometers in from the edge of the ice. Fish and crustaceans were seen in the water, but nothing was spotted in the mud. The lack of mud dwellers might indicate that animals living this far under the ice shelf must be mobile enough to follow intermittent food sources from place to place.

Science fiction short section in Nature describing exploring its ocean in a sub: The ostracons of Europa.

Discovery: Fish Live beneath Antarctica - Scientists find translucent fish in a wedge of water hidden under 740 meters of ice, 850 kilometers from sunlight Earthly Extremophiles Prompt Speculation about Alien Life Priscu is quick to point out that the Lake Whillans microbes were actually fixing carbon about as rapidly as what has been seen in some ice-covered parts of the ocean that are known to harbor fish. “I would be surprised if there are fish [in the lake], but there’s enough energy for them” there, he says. “If we get another grant from NSF, it would be interesting to put down a fish trap and let it sit.” http://www.livescience.com/54756-lake-whillans-antarctica-secret-underworld.html

The General Purpose Heat Source RTG used for Cassini, Ulysses, New Horizons and Galileo generates around 4.41 kW of therma power which means it has about 8.1 kg of Pu-238.. So that's about 38 watts of electric power per kilogram, and about 560 watts of heat per kilogram.

As an example, Curiosity has an RTG with a power output of 125 watts from 2,000 watts of thermal power, and 4.8 kg of Plutonium 238 dioxide (of which Plutonium 238 is 71% by weight). So that's about 26 watts of electric power per kg and 418 watts of heat per kilogram.

Curiosity would need around four times as much Americium 241 as Plutonium 238 for the same power output. However it would continue for much longer at the same power output, centuries instead of decades.

[WHY THIS BIG DISCREPANCY OF ONLY 1 OR 2 WATTS PER GRAM FOR AM241 - AND 23 WATTS PER GRAM FOR PU238? The Planetary society article says 3 watts per kg for Plutonium but I can't make sense of that when Curiosity achieves 23 watts per kg. What am I missing here?]

Some other sources I consulted:

Nuclear Reactors and Radioisotopes for Space
Radoisotopes Power Production - table 2 gives specific power output - i.e. the electricity not heat power - as 0.39 watts per gram for Pu328 and only 0.097 for Am241
ALTERNATIVE FUEL SOURCES FOR RADIOISOTOPE - doesn't give power output but confirms the heat output figures are about right.
Radioisotope thermoelectric generator - wikipedia article
Summary of Plutonium-238 Production Alternatives Analysis Final Report
Can nuclear waste help humanity reach for the stars?
Americium cubesat for interstellar travel
Cubesat 5 watt Am-241 radioisotope heat unit and thermal electrical generator (RHU/TEG)
2013 report - expect 1.5 watts per kg ESA Americium RTG
Frequently asked questions about NASA's use of radioisotope power systems

Then - it's a little harder to understand why he didn't correct that mistake later but it could just be a matter of not drawing attention to something he forgot to say that he felt was not important but could damage his position. Like, painted into a corner.

(using the figures from Can nuclear waste help humanity reach for the stars?):

" Ross proposes a 3 meter long cylindrical sub with an internal diameter of 1 meter. He believes that steel or titanium, while strong enough to withstand the hydrostatic pressure, would be unsuitable as the vessel would have no reserve buoyancy. Therefore, the sub would sink like a rock to the bottom of the ocean. A metal matrix or ceramic composite would offer the best combination of strength and buoyancy."

"Ross favors a fuel cell for power, which will be needed for propulsion, communications and scientific equipment, but notes that technological advances in the ensuing years may provide better sources for power."

"...While Ross proposes using parachutes to bring the submarine to Europa’s surface, McKinnon points out that parachutes would not work in Europa’s almost airless atmosphere."

A submarine for Europa

https://scholar.google.com/scholar?cluster=10022961974803278444&hl=en&as_sdt=0,5

http://users.clas.ufl.edu/prwaylen/GEO2200%20Readings/Readings/Planetary%20formation/How%20was%20early%20earth%20kept%20warm.pdf

(This copy is for your personal, non-commercial use only)

I'll comment on this as usual based on the objective of keeping to close to 100% reliable planetary protection for these icy mooon oceans, rather than the 1 in 10,000 as a "gold standard" approach that's usual in planetary protection discussions at present. If you take that view, an ice mole could still be fine , if we can sterilize them 100%.

http://solarsystem.nasa.gov/docs/Europa_Lander_SDT_Report_2016.pdf

Europa Clipper Mission Concept Preliminary Planetary Protection Approach

Could a Europa lander prepare for a geyser sampling mission?

I think there is little doubt that most astrobiologists would prioritize a geyser flythrough over a lander. See for instance this recent study

"In terms of the search for evidence of life within these oceans, the plume of ice and gas emanating from Enceladus makes this the moon of choice for a fast-track program to search for life. If plumes exist on Europa—yet to be confirmed—or places can be located where ocean water is extruded onto the surface, then the search for life on this lunar-sized body can also be accomplished quickly by the standards of outer solar system exploration."

So, as far as astrobiology goes, a lander, rather than a "win win" situation is a "lose lose lose" situation as far as astrobiology is concerned. There is more to go wrong, the landing itself is risky, it's less likely to sample the ocean, is more likely to be confused by organics from comets and meteorites, if it does find life it is likely to be more degraded, and it needs far more thought when it comes to planetary protection. A lander does make sense at some point, but the natural progression would be to land on Europa a fair while after the first orbits and geyser flythroughs. As someone not involved in any way in the politics, planning and decision making, this idea to land on Europa so soon seems to be driven more by politics than good scientific reasons.

This 2016 report by the VLT found evidence of crystaline rather than amorphous ice. So the ice is likely to be soft like Earth ice, probably as a result of active geology, jets and ice heating.

I think we should leave this option open, what we send to Europa, until we hear back with the first result from the multiple flyby missions. Or even if one component needs its hardware changed to explore some new feature discovered by the previous flyby mission. You still have that option, whether you do it or not. Once your follow up mission is already in flight to Jupiter, there is no way you can do that.

This approach also lets us do a redesign if we find from the flyby missions that it is needed for the Europan conditions.

So why did they send a lander to Titan instead of Europa?

Well there are two other main ways to find a possible signature of life from looking at the amino acids. See the section on amino acid target selection in this paper (about sensitive electrophoresis to examine liquid samples) - which paper?

So why did they send a lander to Titan instead of Europa?

I think it might be partly that they were sending a spacecraft to the Saturn system anyway. In the case of the Jupiter system, then it’s much harder to visit Europa for more than a short time because of the ionizing radiation. Still you could do a penetrator with a fast flyby and that would work much like Huygens. It could communicate back to Earth during the flight to Europa and if it survived the landing, do some experiments and report back during its design life whatever it is.

But it would have many more planetary protection issues to work through than a Titan mission. I think myself it is best to wait for the orbiter mission first before we decide what to do next. We might well confirm the plumes on Europa and that would make it really easy to sample it’s ocean with a low flyby or orbiter and then we might not need a lander at all for the first missions there.

Mission to Enceladus geysers - and identical mission to Europa

Meanwhile one thing we can do right away is to send a mission to Enceladus to analyse its geysers close up, and it would be reasonable I think to send life detection instruments on that mission too. Instruments that would help with analysing whatever is in the particles, able to detect complex organics, and also able to find indications of life too if present.

If funding permitted, perhaps we could also send an identical orbiter geyser fly through mission to Europa “on spec” just in case we find geysers there, to save time. I think that would be less risky than a lander, no danger of crashing, and likely to add to our understanding of Europa even if it has no geysers, by examining the region around Europa just as Cassini did for Rhea etc.

In any case as I said, I think we should equip any Europa orbiter with similar instruments to Cassini which would help with analysing any dust or ice particles or gas around Europa with the capability of detecting complex organics, which may be in them whether or not Europa has life, and I think we should add chirality detection at a minimum. There’d surely be some dust or gas to analyse even if there are no plumes.

There have been several papers suggesting ice in the equatorial regions below the surface. But they are none of them definitive, and though intersting, they don't seem a likely explanation for Viking. But let's just take a look at them. First, ground penetrating radar showed what may perhaps be ice below the surface, in the Medusae Fossae Formation - it's either miles deep layers of equatorial dirty ice or volcanic ash all the way down.. If it's ice then it was probably deposited there when Mars' axis was tilted so far that it had equatorial ice sheets, as happens occasionally - unlike Earth, it's axial tilt varies chaotically on long time periods (as mentioned in Oceans that are only liquid part time as Mars' tilt and orbital eccentricity change (above) ) .

The vertical distance below the surface here shows the radar time delay, roughly corresponding to depth below the surface. Do you see how there is a faint extra line of white in the middle of the picture showing a secondary reflection layer in the radar image? That's the region with probable ice deposits in equatorial Mars. See also Water on Mars May Have Piled Up as Ice Near Equator and for the technical paper Radar Sounding of the Medusae Fossae Formation Mars: Equatorial Ice or Dry, Low-Density Deposits? (abstract). Later research confirms these observations, strongly suggesting that this indicates ice in some form.

It might however be volcanic ash as this paper suggests.

Another set of observations suggested ice at the base of craters in the Sinus Sabeus region, it's mainly evidence that this area had ice in the past, when Mars' axis was tilted more than it is now, but they thought there was a possibility that some ice might still be there today, though buried and hidden from view, concluding (from the paper)::

"It is unclear from available data whether any relict ice is currently present at these locations, although estimates for fill thickness are noteworthy. The equatorial setting suggests that if present, this ice is likely buried by a thick, insulating debris layer or a near-surface layer of reduced permeability."

Another paper suggested there may be still be ice buried beneath the surface in the Valles Marineres region.

More recently, the Mars Reconnaissance Orbiter found a massive sheet of ice in the Utopia Planitia area but that's a much higher latitude, not in the equatorial regions.

if we decide it does need great care, and may contain life hzardous to Earth, we can design the facility on Earth, and pass all necessary laws based on an understanding of what is in the sample. Or we might just continue to study the samples above GEO. Either way we save major expense on designing a facility to handle any possible form of exobiology, and instead design our facility, on Earth or above GEO based on whatever is needed to contain an already studied sample.

Also if we do decide that the material can be returned to Earth in viable form for study as living organisms on Earth, then this will be for a known biology, so the legislation needed could be passed more easily, depending on what is in it.

NASA has an ambitious plan to return half a kilogram of rock samples from Mars in the 2030s, at a cost of many billions of dollars. Many astrobiologists say that these samples are likely to be as enigmatic for astrobiology as the Mars meteorites we already have. Although this mission has a small chance of returning life from Mars, they say that the chances are high that it will be little more than a very expensive technology demo for astrobiology. They say that the best way to resolve the central questions in their field is to do more searches remotely on Mars, "in situ". To them, NASA seems to be "betting the ranch" on a very long shot. This interesting controversy gets far too little publicity, and I cover it in detail.

in studies, books, and reports from international workshops, from the work of Carl :Sagan and the Nobel prize winning microbial geneticist Joshua Lederberg in the 1960s onwards.

- though, note that some scientists think that the other experiments were able to detect ultra low concentrations of life. - this whole field is controversial

(he also gives an interesting analogy there with symbiosis with mitochondria)

And he uses the example of Radiodurans - the microbe which is able to survive in reactor cooling ponds, as an example to show that microbes can survive in environments that they couldn't have been evolved in.

- and powerpoint style slides

, and chroococcidiopsis for 15 months

This is an idea that we've had since Phoenix and its discovery of salts which we know can deliquesce, and discovery of the drops of what looks like water deliquescing on its legs. Unfortunately we didn't have the capability to analyse them, just visual evidence, but is hard to see what else they could be, dark drops that grew gradually, occasionally merged, and eventually drop off. When they dropped off they never formed again at the same spot. Most likely, this shows a process of deliquescence on salt thrown onto its legs during the landing.

Certainly it's a theoretical possibility. Also the Phoenix observation of isotope ratios in the atmosphere show that the CO₂ in the atmosphere must have come from recent volcanic eruptions, and that the oxygen has subsequently changed atoms with some material on the surface, which almost certainly means, dissolved in water. That's good indirect evidence for reasonably abundant water, either thin layers over much of Mars or occasional meltings (e.g. meteorite impacts on the polar regions and high latitudes) or both. Of course both possibilities are of interest for present day life on Mars, but the idea of a permanent layer of liquid water is the one of most promise for the Viking results.

There is some chemical process going on here as the streaks show traces of ferric and ferrous iron. So far nobody has detected water in them, but that might be because they are so thin, well beyond the resolution of their spectroscopic observations, and any water may be in small quantities.

They may also be caused by water which then dries up, or the water may be easier to spot in the morning, perhaps the flows happen in the morning depending on melting frost - the spectroscopic observations were made in the afternoon. See Are These Water Flows On Mars? Quite Possibly, New Observations Reveal

He also makes the rather telling point - how can you say that a Mars microbe can't survive on Earth. when we have a microbe, Radiodurans which was first isolated in reactor cooling ponds? It can't have evolved there as the habitat didn't exist before the 1940s. It's original habitat is in dry lakebeds, quite unlike reactor cooling ponds. Here is his quote:

Also, did you know that there are at least two places in the solar system where humans don't need a fully pressurized spacesuit? These may have no planetary protection issues at all (though it needs further study).

What happens to all our plans to explore the red planet, if we decide not to touch it quite yet? Well, we can continue to touch it remotely, with our robotic hands and eyes on Mars, They will get faster and more capable, and we should get broadband streaming back to Earth, of hundred of gigabytes of images a day, in the mid 2020s. That will be a dramatic change. Meanwhile our astronauts can start on the Moon, which has turned out to be much more interesting than expected. It has ice at the poles right next to almost continually sunlit peaks. We should find meteorites there from early Earth, Mars and perhaps even Venus, wonderfully preserved, deep in the extremely cold ice, that never see a ray of direct sunlight. Later, as we learn safe ways to send humans further afield, they can go to Mars orbit, and its moons, with no biological impact on Mars yet. They can explore its surface in immersive 3D. All of us back on Earth can join in, exploring a fantastically detailed landscape built up from hours of binocular HD video streamed from many locations on the surface every day. Our robots can also explore the oceans of Europa and Enceladus, and more exotic places, ranging from the molten sulfur lakes of Io through to the liquid nitrogen geysers of Triton.

It would be different if they said in the summing up: "We also read a white paper from eight astrobiologists but we ignored it because of ...". If they thought it didn't need to be discussed, why couldn't they have explained why they thought it should be ignored? But they gave no reason for ignoring it. So we just have to leave this as a mystery unless anyone reading this happens to know the answer.

During the Q / A, the team mention the idea of sending in situ life detection instruments to Europa in the future. We could use these on a flyby or a lander. So what instruments could we send? Actually there are many such already developed. Some of them have exquisite sensitivity, and could find life based on the minutest of traces, even able to detect a single molecule in the sample of biochemical interest.

The problem is the huge cost, millions of dollars per gram. All this funding for a Mars sample return mission is funding taken away from other missions including in situ studies on Mars.

We may have to do extensive in situ searches on Mars before we find the right samples to answer our questions about whether life ever evolved on Mars and whether it has life at present. If the astrobiologists are correct, then sample return is not the best way to do that, because you'd have to return an unfeasible amount of material to Earth at huge expense to make much progress..

It's also based on the idea that we already know enough to select suitable sites for a sample return.

only two years after this report, eight astrobiologists submitted a white paper to the decadal review strongly urging that we do in situ searchers first. They expect the search for Mars past life to be hard, as hard as the search for microbes in ALH84001, in the paper I covered already above in Follow the nitrogen, dig deep and look for biosignatures.

Artist's impression of the five planet system around Tau Ceti. Credit: J. Pinfield for the RoPACS network at the University of Hertfordshire Most of its planets seem likely to be uninhabitable, but one of its planets is well within the zone (planet f) and it probably moved into the habitable zone in the last billion years. Tau Ceti is an orange dwarf star. That's a more common type of star than our Sun, and research so far suggests they may be very habitable stars.See this recent survey of the literature: The Habitability of Planets Orbiting M-dwarf Stars

New ideas suggest that planets huddling close to red dwarf stars could be habitable, even though they would be tidally locked with one side always facing to the parent star. This is by far the most abundant type of star in our solar system. However other research suggests that planets, huddled so close to their parent star, also face more intense UV and X-Ray emissions than our Sun, that may denude the surface of oxygen and water within a few million years.

Whether it was a red dwarf, an orange dwarf, a yellow dwarf like our Sun or some other star, it would just take one of these stars, with its planets already seeded with life passed through the star forming region where our sun was born, to seed the entire region.

Perhaps it was a smaller red or orange dwarf stars, as those are far more common, and as for yellow dwarfs like our sun, and even more so, they are especially stable and long lived.

Artist's impression of three planets orbiting a red dwarf star. New ideas suggest that planets huddling close to red dwarf stars could be habitable, even though they would be tidally locked with one side always facing to the parent star. This is by far the most abundant type of star in our solar system. However the planets, huddled so close to their parent star, also face more intense UV and X-Ray emissions than our Sun, that may denude the surface of oxygen and water.

Whether it was a red dwarf, an orange dwarf, a yellow dwarf like our Sun or some other star, perhaps a a star with its planets already seeded with life passed through the star forming region where our sun was born.

he 2012 ESA study of a Mars sample return in its section 2 has a list of some of the most important pros for sample return, citing this study. To paraphrase some of their list of pros, with responses:

In situ experiments will be too complex for an in situ mission and will have major limits of size and weight
- response: as we'll see, these issues have mainly been dealt with. There are many in situ experiments to search for life that are either already space ready or could be made so quickly with enough funding
Returning a sample allows one to respond to the unexpected with new protocols and experiment
- response - but in situ allows you to respond to the unexpected in a different way - by following up in situ. If you have a versatile suite of instruments, then it can be used in original ways in situ. As an example, , Cassini, because it had such a well thought out suite of instruments, was able to do follow up studies of the geysers of Enceladus, a phenomenon tha twas never predicted by its designers. So spacecraft too, through ingenuity, can be used in unexpected ways. If

Additionally, if we find some unusual feature on Mars also, we can go look in situ. If we return something interesting and decide we have to have information about a rock just next to it on Mars, we have to send a new mission ot Mars to look at it
Ability to repeat in multiple laboratories to confirm results
- response - yes that's an advantage - but the downside is that you have only a few grams of material to share with those multiple laboratories, and they can't access any more material from Mars except by spending billions of dollars for another mission.
Everyone can take part in invesigating it
- response - well with an in situ search, everyone can pore over the images and returned data, and make suggestions.
We can propogate the organisms if any life is returned
- response - yes but first we are probably unlikely to return any present day life from the locality of Curiosity 2020, unless present day life is very abundant. If Curiosity2020 can't detect the life in situ, it could sample a patch of rock without life just next to a patch with life, and we'd never know what happened. And if it does find life, it could die during the journey back.

Well, yes, that's the idea nowadays. We do have many in situ instruments that would be able to detect if there is life on Mars. Some instruments still can't be miniaturized. We can't miniaturize particle acclerator mass spectrometers. Yet, our spacecraft have been able to distinguish isotopes using other forms of mass spectrometry.

If an experiment can be miniaturized, it might take a fair bit of work to do,, but it would still probably cost much less than the sample return. Then there's the plus side that you'll be able to study the samples in pristine conditions in situ. You'll also have a new instrument you can use in all future missions to Mars and other destinations in our solar system. Also, many of the instruments you'd want to send have already been miniaturized. There have been major breakthroughs in the miniaturiziation of all sorts of instruments, indeed nowadays they can design some of the Mars in situ instruments mainly by combining off the shelf commercial devices which were developed only in the last few years. See the section In situ instrument capabilities below for details.

I've covered their paper already above in Follow the nitrogen, dig deep and look for biosignatures. So they expect the search for Mars past life to be hard, as hard as the search for microbes in ALH84001. With that background and the complex geology of Mars, it's not at all clear that we can hope to find evidence of past life on Mars easily, or at all, by sample return missions. Not unless we already know it is there, and know where to look, and what to return. Indeed, as we'll see in a minute in the section Astrobiologists arguing strongly for an in situ search on Mars first, they think the samples returned in this way, so soon, might well settle nothing and just lead to more debate and uncertainty in astrobiology, similarly to the never ending debates we have about the Mars meteorites we already have. With that background perhaps you can understand why they aren't gushing over with enthusiasm for a sample return.

early life enthusiasts rather than fossil optimists, as I covered in Fossil optimists and early life enthusiasts (above) .They don't want to pin all their hopes on the possibility that Mars had abundant easy to spot comples life already billions of years ago. That may even seem rather unlikely given how tough conditions were on Mars, with the oceans freezing over every Martian year probably and most likely even those summer oceans were only habitable for tens of thousands of years at best. Also, present day life is likely to be elusive and hard to find too as we've discovered. So, they just don't think that past or present day life will be as easy to find as the other space scientists seem to think. They don't think it will be so simple, that you just send a rover there, it searches for organics, picks up some rocks, and this settles the most important questions in astrobiology about Mars.

Huge disconnect between astrobiologists and decision makers

I can't find any recent comparison study between an in situ search and sample return. The 2012 ESA study of a Mars sample return in its section 2 has a list of some of the most important pros for sample return, but doesn't mention its cons, or the pros of an in situ search or its cons. It refers to a 2007 study which does give a list of the pros and cons of each one. But this is from a while back - a lot has changed in the last decade.

The ESA's list of pros, to paraphrase are:

In situ experiments will be too complex for an in situ mission and will have major limits of size and weight
- response: as we'll see, these issues have mainly been dealt with. There are many in situ experiments to search for life that are either already space ready or could be made so quickly with enough funding
Returning a mission allows one to respond to the unexpected with new protocols and experiment
- response - but in situ allows you to respond to the unexpected in a different way - by following up in situ. Example, Cassini, because it had such a well defined suite of instruments, was able to do follow up studies of the geysers of Enceladus, a phenomenon tha twas never predicted by its designers. So spacecraft too, through ingenuity, can be used in unexpected ways. If we find some unusual feature on Mars also, we can go look in situ. If we find something intersting is returned and we decide wewant information about a rock just next to it on Mars, we have to send a new mission ot Mars to look at it
Ability to repeat in multiple laboratories to confirm results - yes that's an advantage - but it hasn't been a major issue with space exploration so far. Except Levin's labeled release. But in an example like that - the life might well be dead already by the time it gets back to Earth.

Many experiments and their sample preparations will be too complex for an in situ robotic mission
Returning a sample allows for flexibility in deal - ing with the unknown and unexpected discoveries via new protocols, experiments and measurements
There are major limitations with regard to size and weight of instrumentation that can be flown
There is a significant communication delay to Mars, which impedes the ability to deal with emergencies
There is a much greater diversity in available instruments and an almost unlimited range of analytical techniques that can be applied on Earth
The ability to repeat experiments in multiple lab - oratories and confirm key results is available on Earth
Participation of entire analytical community is possible
There is the potential to propagate organisms if they are discovered

In addition to the above points, returning a Mars sample will bring enormous public excitement and engagement to space-related activities, along with pride and prestige to this accomplishment of man - kind.

However, the

Surely someone needs to do a comparison study before such expensive decisions as to commit NASA to two flagship missions one after another? And the same for the other equally expensive missions by other space agencies? Well, it turns out that a group of eight astrobiologists did. And what's more they did this in a white paper submitted to NASA decadal survey itself. And what's more, this study comes out firmly in favour of in situ exploration, and strongly against a sample return, at least as far as the search for life is concerned.

The only comparison studies I know of are the ones by the astrobiologists, and they all come out firmly in favour of in situ exploration and against a sample return. Yet NASA motivates the sample return as our best way to make progress in astrobiology. Surely the astrobiologists, of all scientists, are keenest to find out about Mars life, if it exists?

Well it's because astrobiologists tend to be early life enthusiasts rather than fossil optimists, as I covered in Fossil optimists and early life enthusiasts (above) .They don't want to pin all their hopes on the possibility that Mars had abundant easy to spot comples life already billions of years ago. That may even seem rather unlikely given how tough conditions were on Mars, with the oceans freezing over every Martian year probably and most likely even those summer oceans were only habitable for tens of thousands of years at best. Also, present day life is likely to be elusive and hard to find too as we've discovered. So, they just don't think that past or present day life will be as easy to find as the other space scientists seem to think. They don't think it will be so simple, that you just send a rover there, it searches for organics, picks up some rocks, and this settles the most important questions in astrobiology about Mars.

Everyone agrees that a sample return would be great for geology. But what are the implications for NASA's plans, if they go ahead with this, and return samples at great expense, and the astrobiologists then say that they are of no more value to astrobiology than one of the Mars meteorites? Surely this will be a huge embarrasment for NASA. It's not the fault of the astrobiologists as they have warned about this over and over. As we'll see, many other astrobiologists have also published papers arguing very strongly that a sample return is just not the way ahead right now for their discipline.

There is a huge disconnect here when you read the literature on the subject. There are many articles by space scientists discussing sample return missions. They work on minute details of the sample return spaceraft, heat shields, sample receiving facility and so on. They write pages and pages of material on these matters. But these papers and studies, without exception, take it for granted that a sample return is the best way to search for life on Mars. They might give. at most, couple of motivating paragraphs, describing how we can do analyses here on Earth that we can't do in situ. But they treat it as a settled mater, as if there had been an investigation that determined this for once and for all. There hasn't.

It's obviously true, that there are some experiments we can't miniaturize and send to Mars at all, especially the ones that involve large particle accelerators to find the age of the samples. Indeed, that's the usual one mentioned, and I don't actually know if there is any other experiment that couldn't be miniaturized and sent to Mars. This is the only one I've seen mentioned in the literature.

If an experiment can be miniaturized, it might take a fair bit of work to do that, but it would still probably cost much less than the sample return. Then there's the plus side that you'll have many more samples to study in pristine conditions in situ. You'll also have a new instrument you can use in all future missions to Mars and other destinations in our solar system. Also, many of the instruments you'd want to send have already been miniaturized. There have been major breakthroughs in the miniaturiziation of all sorts of instruments, indeed nowadays they can design some of the Mars in situ instruments mainly by combining off the shelf commercial devices which were developed only in the last few years. See the section In situ instrument capabilities below for details.

So how important is it that we can put the samples in a particle accelerator to stuidy their ages? Especially given that we can already do that with the Martian meteorites. Is that worth the price tag of millions of dollars per gram? And if not, is there anything else we can do on Earth that is so compelling that it justifies the price tag?

The proponents of a Mars sample return never discuss this. Also, they never mention the arguments of the astrobiologists. And it's not just NASA that's prioritizing sample return from Mars in this way. They are just the first off the block. Other countries that may do a sample return in the near future include Russia who plan a Phobos sample return (again) (which is much easier to justify financially as it costs a lot less), but hope to do a sample return from Mars in the 2030s, Then there's China who aim for a sample return mission around 2030, and indeed the ESA themselves just mentioned, who have explored the idea for many years.

It's become the "received wisdom" world wide that a sample return from Mars is our next priority. The obvious thing to do would be to have a major comparison study of the two approaches, in situ, and near future sample return. We could do it under the auspices of the National Research Council, or the European Space Foundation, simlarly to the studies we've had already about back contamination safety issues for a sample return. But we haven't had anything like that. The sample return studies that they have done all take as a given that we will do a sample return and it's above their paygrade to ask whether this is a good thing to do.

So, on this topic, we just have the papers by the astrobiologists. There simply aren't any published replies arguing the case in the opposite direction as far as I can tell. There are no published counter arguments, and no independent studies. They are just ignored.

So it's hard to know what to do. I can't present both sides of the argument as essentially there is no published argument in favour of a sample return, except the argument about particle accelerators which is not done as comparison study, but as an example, as if that one example justified everything..

So, what I'll do is just explain why it is the astrobiologists think that a sample return is not the way to go right now, and leave the question open. But if I can comment, I strongly recommend that someone looks at this in more detail and finds a wya to do an independent review of this, before we spend more billions of dollars on a sample return, that might not be what we need at present.

So - if you had large very productive areas as productive as the biomats in Antarctica, covering an entire square kilometer somewhere on Mars, then TGO could detect the 89 grams per square kilometer it adds to the atmosphere. But to detect the faint signal from a sparse habitat such as the RSL's seems to be right at the edge of its capabilities and probably beyond it, if they are only surface habitats. This is just a crude approximation. I was surprised to work out that it can detect concentrations as low as a few grams per square kilometer. Especially if the processes are not continuous but produce larger quantities of organic gases in the atmosphere over a short period of time, perhaps built up over years then released all in one go,I wonder if it has a chance of detecting life there?

We can get some idea of this from measurements of microbial mats in ice covered lakes in the dry McMurdo valleys in Antarctica. These measurements were taken in Lake Hoare.

Lake Hoare (Antarctic explorers)
Benthic Microbial Mats Ice-Covered Antarctic Lakes

The researchers estimated that the microbial mats in this lake produce 0.089 micrograms of oxygen per square centimeter of surface per hour. There are 10 billion square centimeters in a square kilometer and a billion micrograms in a kilogram so that works out as 0.89 kilograms per square kilometer per hour, of oxygen, or around 325 kilograms per square kilometer per year. See Photosynthetic performance of benthic microbial mats in Lake Hoare, Antarctica

For methane on Mars it is 430 years - a lot longer than on Earth, but on Mars there's almost no oxygen to react with it.

All other spacecraft like Pathfinder, Opportunity, Spirit, Phoenix, and Curiosity, they sterilized them to the pre-heat treatment stage on Earth for Viking. Then they count on the harsh environment on Mars for the rest of it.

You might expect astrobiologists to be the ones most keen on this sample. But no, they argue strongly against spending space exploration budget on this, at this stage. That's because they expect samples returned from Mars to be just as controversial and hard to interpret as the Mars meteorites we already have. We may have to do extensive in situ searches on Mars before we find the right samples to answer our questions about whether life ever evolved on Mars and whether it has life at present. Sample return is not the best way to do that, because you'd have to return an unfeasible amount of material to Earth at huge expense.

(as well as to make room for the Moxie instrument which tests production of oxygen in the Mars atmosphere from CO2 and has no immediate science values for study of Mars)

None of this would matter if Mars was so different from Earth that no Earth life could survive there. For instance, temperatures on Titan are well below the temperatures for Earth life and the only water is thought to be in the form of solid rock, while the fluid is ethane or methane. There would be no issues with contaminating Mars if conditions there were like Titan (and assuming no cryovolcanism - volcanoes with liquid water as lava). That really would be like Robert Zubrin's analogy (see Sharks in the savannah or rabbits in Australia? (above))

But no, it's actually rather habitable for Earth life - for extremophiles that is.

All these are places we can explore by telerobotics using increasingly capable robots, also explore using robots controlled from Earth. There is no need to send humans to these places as quickly as possible. It won't help to make us multiplanetary, but it may mean we miss out on discoveries about the origins of life, and other lifeforms.

If we introduce Earth microbes to them, accidentally or intentionally, this may well be irreversible. It's the irreversibility that's the issue here. If it is biologically reversible, not so much of a problem. But if irreversible, that means it would change those places for all future time, not just for us, but for our descendants and all future civilizations that arise in our solar system, they won't be able to make the discoveries they could make by studying these places as they are now, without Earth microbes introduced to them. They also won't be able to transform them in other ways if they decide they wish to introduce a different mix of microbes from the ones we brought there.

I think we just know far too little to make such a decision for all those future generations and civilizations and indeed for ourselves. At present anyway. Future discoveries of course can change this.

This search for extra terrestrial life is the aspect of our exploration of the solar system that gets most interest of all from the general public I think. And if we did find an early form of life, or something significantly different, it would be the greatest discovery in biology since the discovery of evolution, or perhaps the discovery of the helical nature of DNA, of that order of importance. Who knows what implications it would have, if you think of how much of modern biology comes from those two discoveries.

The paper is here (but behind a paywall).

For some of the others, see my book:

Well suppose for instance that the radiation was strong enough to kill half the organisms in a hundred thousand years. Then after two hundred thousand years there'd be only a quarter left, and it halves every hundred thousand years. After a million years there'd be only a thousandth of the original organisms still viable. After two million years, only a millionth, and I think you can see that after a few million years, there'd soon be nothing viable left at all.

What's changed is that before 2008 they were talking about dormant life.

, in one of the models, fresh water trapped below a clear ice solid state greenhouse, the water will certainly be both warm enough and fresh enough for life. The interfacial liquid layers also seem promising because of the way the models predict them to flow together into a liquid stream of fresh water that then picks up salts on its way out, so these also might be habitable.

No, it's fake news, of the silliest kind. The original story talks about the "dark side of the sun" but after a week or two of repetition from one way out blog to another, it morphed into a new story without that detail. At that point it took off and got repeated in all the tabloids and other magazines with no checks in place for fake news. Debunked here. Debunked: 2016 WF9 to hit Earth and trigger mega-tsunamis next month

They speculate about whether lack of nitrogen could have made present day life on Mars extinct.

The 5 mbar level there is far lower than the present day levels for Earth's atmosphere of 781 mbar. Also they only studied normal non extremophile nitrogen fixators. An obvious follow up experiment would be to do the same tests, but with Antarctic nitrogen fixating extremophiles. The authors of this paper propose it as an experiment to do that, but as far as I can see, haven't actually tried it. In their preprints here and here, they did preliminary experiments to test other stresses but don't seem to have done the experiment with the extremophiles at Martian atmospheric pressures and levels of nitrogen

If anyone here knows of research on the limits of low pressure nitrogen fixation for extremophiles, do say. It seems a bit of a stretch. Perhaps the answer would indeed be "No". But iff photosynthetic life could do nitrogen fixation in the Mars atmosphere, then if combined with the ability to take up water from the night time humidity, almost the entire surface of Mars would become available in partially shaded patches for protection from UV.

Another paper studied a present day Mars atmosphere but under full Earth pressure and found plenty of evidence of nitrogen fixation. - not much use

"Aquifers as shallow as 100 m below the surface might exist on Mars. Possible combinations of the typical geothermal heat flux with a thick, low-conductivity and sufficiently permeable regolith, result in the melting of ice this shallow, allowing the formation of aquifers. This is extremely important because aquifers could support biological activity. Groundwater has not been detected unambiguously on Mars yet, but rheological features such as gullies have been hypothesized to form by the discharge of shallow aquifers."

The interior of a cell is so complex it's been compared to an entire ecosystem. So life based on different principles could be as revolutionary for biology as discovering a coral reef for your first time, when the only ecosystem you knew about before is the African Savannah. I make this analogy here: "Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And Enceladus

Schiaperelli crash site on Mars. Upper image shows the point of impact. Lower left is the parachute and lower right shows its rear and forward heat shields, photographed from orbit by HiRISE aboard Mars Reconnaissance Orbiter

Created by life, from raw ingredients. For instance, in the case of photosynthetic life, a "primary producer" like Chroococcidiopsis just needs sunlight, carbon dioxide, water, nitrogen from the early Mars atmosphere, and trace elements to create organics. This then can be eaten by secondary consumers on Mars

That's because the Mars atmosphere gives little protection from cosmic radiation. This radiation has little effect over thousands of years, but over millions to billions of years timescales even large quantities of organics get broken up into water vapour, methane, carbon dioxide etc. This could easily degrade it beyond recognition through cosmic radiation.

It gets supplied by organics from meteorites, comets and created in volcanic processes. These would get mixed with the organics from life which we are looking for. And to make things more confusing, the meteorites often have a chiral signature.
Chiral excesses in the meteorites (covered above)
Early life might even have been ambidextrous (non chiral) (covered above)

So, this research suggests it is likely to be far more difficult to find past life than you might expect. It's no surprise that Curiosity hasn't found it yet - it is just not looking in the right way in the right place. Indeed, it's not searching for past life, that's not its main mission. It's searching for past habitability, a brief that it has fulfilled rather well. But the organics it has found already are thought to have come from meteorites or comets.

When the team selects samples for Curiosity 2020 to return to Earth, they are almost certainly going to come from those as well. Perhaps you can begin to see already why astrobiologists think it's unlikely that we will find traces of past organics unless we do an in situ search for life and unambiguous biosignatures on Mars itself.

But let's look at this a bit closer. What is

So now imagine trying to disentangle all that while studying ancient Mars deposits that have had any chiral signature very much degraded by just being there for billions of years, and also perhaps mixed in with later life and organics from meteorites and comets. And maybe it didn't even have a chiral signature originally. Now add in a signal from present day Earth life. That's going to make it vastly more confusing to figure out what happened. Again the task is hard enough as it is, and we don't want to make it even harder.

The main problems here are that the organics can be degraded by many processes on Mars. Also, they may have been present only in a few favoured spots originally, and the search is confused by a constant influx of organics from meteorites and comets which may have chemical signatures that mimic some life processes.

There's also a lot of research into semi-synthetic minimal living cells. Some start with vesicles and try to insert the replication machinery of a modern cell into them. Other approach is to start with a modern cell and insert reduced size DNA or synthetic DNA into it.

First let's summarize the situation, then I'll go over it in more details. It is really hard for a microbe to get from Earth to Mars. The new research that suggests it is possible after all is rather a remarkable discovery.

Most microbes that could get to Mars on a human occupied spaceship, and perhaps survive on Mars once there, would probably never get there in a meteorite. Also it's not easy for life that gets there in a meteorite to find a suitable habitat, because the surface is so dry and cold, laced with perchlorates and hydrogen peroxide with not much by way of habitats and any microbes would probably get there buried deep within a rock as we'll see. The most likely time for microbes to get from Earth to Mars is in the early solar system, over 3.75 billion years ago, soon after formation of the Moon, and it is challenging even then, as it turns out that most would not survive the shock of being ejected from Earth. By far the easier direction is from Mars to Earth, but that direction also is still a huge challenge for most lifeforms, and of course we don't yet have any proof that it has ever happened in either direction.

Also, suppose a photosynthetic lifeform from Earth spreads over most of Mars, able to survive just in the night time humidity, then theis could take more carbon dioxide out of the atmosphere, making it even thinner, and cooling down the planet further.

It turns out that photosynthetic microbes find it harder to survive transit on a meteorite than some the species studied. Yet

Modern life may be scarce and hard to find, because the conditions are so inhospitable. It would be life at the edge, only just surviving. A few stray spores from Earth would be all that was needed to hide the signal altogether, even if the spores don't reproduce there. While reproducing spores from Earth would be an end to pristine Mars.

Past life may have been destroyed long ago except in a few favoured patches. There may have only a few trace amounts of organics from the past mixed with organics from non life processes, as we'll see.

It might also be early life (in both cases), that hasn't yet evolved to be as large as modern microbes on Earth. It might also be based on different biological principles from Earth life. If so, we have to find ways to detect it that don't rely on it having an identical biology, and again that will be hard to do if the signal is overwhelmed by organics and viable spores from Earth.

As for viable present day microbial spores mixed in with the dust, we could detect them, but we haven't yet sent anything to Mars with enough sensitivity since Viking. One of the Viking experiments was actually way ahead of its time in its sensitivity. Gilbert Levin's labeled release experiment was exquisitely sensitive, as it could detect microbes, even if the microbes didn't reproduce, so long as they revived and started metabolizing. Though we have many other ways to search for life now, to this day it would still count as an extraordinarily sensitive experiment.

But sadly the unusual chemistry on Mars involving perchlorates cast doubt on their results. For some reason, despite many attempts to get this experiment on later rovers, we haven't sent the obvious follow up to check up on it. That would be a chiral labeled release experiment which would settle this once and for all.

The idea is that all Earth life can only use molecules such as amino acids in one form. The mirror image of the same moledule is inedible. They expect biochemistry to work similarly on other planets even if not related to us. So the idea is to use nutrients that are identical in all respects except that you feed the dust with mirror image molecules. If the Viking results were due to strange chemistry that should make no difference, and if it is life that caused the Viking results, you will spot that because nothing will happen if you use the mirror image molecules. It's the obvious experiment to do next, also very low mass and low in power requirments, but neither NASA nor ESA seem to be interested in flying it to Mars at present.

This experiment is very sensitive. But of course it would be confused by any Earth spores that got to Mars. It would detect them as "life" and it can't distinguish between life from Mars and life from Earth except by virtue of doing the experiment on Mars. Also, this experiment will only work if there is life in the dust, and able to survive and metabolize in the culture medium. If Viking found life, then this experiment should work. If not, it doesn't disprove life on Mars, just shows that it is hard to find. I go into this whole thing a lot more in the section Rhythms from Martian sands - what if Viking detected life? (below).

One of their experiments, the Viking labeled release, was way ahead of most biological instruments of its time in sensitivity. It was able to detect microbial respiration from just a few cells, even if they couldn't reproduce in the culture medium. This experiment seemed to detect life but could have been confused by the unusual chemistry of the Mars soil, which nobody expected. There is an obvious follow up experiment to test for that. Many organic molecules come in two mirror image forms, and modern Earth life can only eat one of them - for much the same reason that all DNA spirals the same way. The mirror image chemical is inedible. Astrobiologists think that even unrelated life on another planet is likely to work in a simlar way. So the obvious follow up is to send an experiment with chemicals of only one type, then try the mirror image chemical in its place and see if there's a difference. If what Viking found is life, then it won't be able to eat the mirror image chemical, while if it is just chemistry it should make no difference.

It's the same the other way around for any Mars microbes that may be able to survive on Earth. Native Mars life could easily be so harmless that you could eat a kilogram with no ill effects (as Carl Sagan put it in chapter V of Cosmos), but in the worst case it could impact in various ways on the environment of Earth itself, and make it less habitable for our native life. For this, and other reasons, astrobiologists recommend that we take great care if we return unsterilized samples from Mars, at least until we know what is in them. More about this in Safe return of an unsterilized sample below.

http://www.e-reading.club/book.php?book=1010313 - Cosmos

http://www.e-reading.club/chapter.php/1010313/6/Sagan_-_Cosmos.html - chapter about sample return. .

The surface area of Mars is exactly as large as the land area of the Earth. A thorough reconnaissance will clearly occupy us for centuries. But there will be a time when Mars is all explored; a time after robot aircraft have mapped it from aloft, a time after rovers have combed the surface, a time after samples have been returned safely to Earth, a time after human beings have walked the sands of Mars. What then? What shall we do with Mars?

There are so many examples of human misuse of the Earth that even phrasing this question chills me. If there is life on Mars, I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes. The existence of an independent biology on a nearby planet is a treasure beyond assessing, and the preservation of that life must, I think, supersede any other possible use of Mars. However, suppose Mars is lifeless. It is not a plausible source of raw materials: the freightage from Mars to Earth would be too expensive for many centuries to come. But might we be able to live on Mars? Could we in some sense make Mars habitable?

For some reason NASA has no interest in flying this chiral version of the labeled release experiment. Russia was interested. They wanted to fly it to Mars in 1996 on their Mars 96 probe. But the experiment was descoped. According to Barry DiGregorio, NASA convinced them not to fly it by paying them millions of dollars to fly their Mars Oxidant experiment instead. This was an experiment to test for reactive chemistry on Mars that could have confused the Viking results. Levin was invited to participate in it, and added two chiral fiber optic sensors that would have yielded some more information about the labeled release experiment. Sadly Mars 96 failed on launch. The second burn of its fourth stage failed when it was already nearly in orbit, and it crashed back to Earth.

At any rate whatever the reason for this, the result is that the Viking labeled release experiment has had no follow up, and it's still possible to hypothesize that Viking discovered life on Mars. The instruments on the Curiosity rover are not nearly sensitive enough to disprove this. Though this hasn't been proven, it's not been disproven in a scientifically rigorous way either. For more on this see Rhythms from Martian sands - what if Viking detected life? (below).

Geological eras on Earth are recognized by the dominant lifeforms in them. If some Earth microbes survive on Mars, and spread, irreversibly, this could create a new geological era, with Earth life dominating the biology and any processes that involve habitable liquid water throughout the planet.

Humans on the surface could even start a new geological era on Mars, with Earth life dominating all habitable water on Mars,- if they introduce Earth life irreversibly, and depending on how Earth life interacts with any native Mars life.

What if it is a very rare phyla and species that happened to get to Mars on one of the early flights to Mars?

To show how hard it would be to characterize the microbial inventory of a human mission to Mars, in one study of the population of microbes in 60 samples taken from belly buttons of humans, they found 2368 distinct species. Of those, 2188 were present in less than 10% of the sample and most were present on only one individual.

At any rate the studies into risks of a sample return from Mars have all concluded, to date, that we do have to take care, for this reason. That the chance of harm to Earth is probably very low, but we have no way to assess the risk as a probability. Until we know what we are likely to return to Earth, we need to design the sample return to be sufficiently robust and safe to contain any possible form of exobiology that we might find on Mars. That is tricky to do, since we only have the example of Earth life. So how can we design to contain any possible form of extraterrestrial life when we have only the one example? It would be much easier if we knew what we were going to return first.

If it was a hyper velocity impact, then it could immediately send debris as far as a thousand kilometers away from the impact site, as Carl Sagan and Elliot Leventhal pointed out in their 1967 paper "Contamination of Mars" (discussing unmanned probes to Mars). That's especially a risk if they land with supersonic retropropulsion, so not in a capsule designed for aerobraking if the landing fails.

If only we were like plants, so that you could grow us from sterile seeds. But we can't survive without the many trillions of microbial hitchhikers in many thousands of species, that travel with humans wherever we go. The astrobiologists who have looked into this can't yet say for sure that our microbes will play nicely on Mars. If some of them survive there, in the worst case they could create a new geological era on Mars, with Earth life dominating any processes that involve liquid water throughout the planet. .

For another Mars related example, Kim Stanley Robinson's "Mars Trilogy" has many points where the numbers are fudged in order to create a gripping story line. He needed the process to be completed within a few generations. For instance, supposing there is enough carbon dioxide on Mars (not known), Chris McKay, in one of his papers, estimates that it would take 100,000 years for photosynthesis to fix enough carbon from the atmosphere to build up the meters thick layers of peat, wood etc over its entire surface needed to make it an oxygen rich atmosphere.

For another Mars related example, Kim Stanley Robinson's "Mars Trilogy" has many points where the numbers are fudged in order to create a gripping story line. For instance, supposing there is enough carbon dioxide on Mars (not known), Chris McKay, in one of his papers, estimates that it would take 100,000 years for photosynthesis to fix enough carbon from the atmosphere to build up the meters thick layers of peat, wood etc over its entire surface needed to make it an oxygen rich atmosphere. It takes longer on Mars because in the low gravity, you need more mass of oxygen for the same partial pressure, and you also have only half the amount of sunlight as Earth. Kim Stanley Robinson needs all this to happen within a few generations, for dramatic effect. So, as science fiction writers so often do, he uses "poetic license". He fudges the science, for the sake of a good story. Hoperfully most readers understand that, but in online discussions, you do get people who treat his novels as if they were hard science predictions. They assume that it would be feasible to turn Mars into a planet like Earth in a few centuries, with just a small amount of technology plus adding life to the planet.

Of course Mars might well already have photosynthetic native life, and if so, it hasn't made it into an Earth-like planet, and why should it? We tend to accept this as an eminently sensible idea because it fits the familiar trope of automatic terraforming (see below). But on Mars, photosynthetic life would cool down the planet and make it less habitabley, the opposite of what it does on Earth where photosynthesis helped to prevent Earth getting too hot, and keeps it habitable. Indeed, if I can offer a suggestion, what if it is self limiting? What if, every time Mars develops too much photosynthetic life, the planet cools down until there is a small enough amount of life left for it to remain habitable, as a kind of "anti Gaia"? In that case - what good would it do to introduce Earth photosynthetic life to Mars? At any rate, Mars is too cold to have trees and ice free water, even with Earth pressure carbon dioxide and without an oxygen rich atmosphere, and iy'd far too cold to be Earth-like without artificial help. Published suggestions on how to terraform Mars assume megatechnology, long term, in the form of planet sized thin film mirrors or continuous production of potent greenhouse gases, or both, to keep the planet warm.

For another Mars related example, Kim Stanley Robinson's "Mars Trilogy" has many points where the numbers are fudged in order to create a gripping story line. For instance, supposing there is enough carbon dioxide on Mars (not known), Chris McKay, in one of his papers, estimates that it would take 100,000 years for photosynthesis to fix enough carbon from the atmosphere. The thing is that to build up oxygen in the atmosphere, you have to take out the carbon. It just takes a long time to build up the meters thick layers of peat, wood etc over its entire surface needed to make it an oxygen rich atmosphere. Kim Stanley Robinson needs all this to happen within a few generations, for dramatic effect. So, as science fiction writers so often do, he uses "poetic license", i.e. he fudges the science, for the sake of a good story. Of course Mars might well already have photosynthetic native life, and if so, it hasn't made it into an Earth-like planet, and why should it? We tend to accept this as an eminently sensible idea because it fits the familiar trope of automatic terraforming (see below). But on Mars, photosynthetic life would cool down the planet and make it less habitable, the opposite of what it does on Earth where photosynthesis helped to prevent Earth getting too hot, and keeps it habitable. Published suggestions on how to terraform Mars assume megatechnology, long term, in the form of planet sized thin film mirrors or continuous production of potent greenhouse gases, or both, to keep the planet warm.

Arthur C. Clarke in one of his best early short stories, not before the lunar landing, describes the Moon covered with fine dust so deep that rovers could sink into it without trace. All the early stories had oceans on Venus, and Mercury with one face permanently facing the sun. Early stories are a mix of far future technologies we don't have yet with what we now see as retro future ideas such as explorers using slide rules in spaceships that travel faster than light. (Full text)..

The Mars trilogy and Mars colonization stories are bound to seem similar to future readers - a mix of the astonishingly prescient with the bizarrely out of date and just plain wrong.

The first papers on planetary protection, in the 1960s, were by Carl Sagan and Joshua Lederberg,who got the Nobel prize for his pioneerign work on microbial genetics. We've had numerous workshops and detailed studies since then, and they all come to the same conclusion, that Mars life if it exists could potentially be vulnerable to Earth life and vice versa. There are hardly any dissenting voices, but one of them is Robert Zubrin, space engineer and leader of the Mars Society, and a keen advocate for Mars colonization. He pours scorn on the idea of all these astrobiological experts, that we need to do anything at all to protect Mars or Earth, and he has arguments that his followers find convincing. If you have ever discussed this with Mars colonization enthusiasts, or you are such an enthusiast yourself, you have probably come across them.

His four main arguments are:

Earth life can't compete with native Mars life - it would be like sharks competing with lions in the Sahara because the planets are so different
Any Earth life that could survive on Mars is already there, transported on meteorites
It will be easy to distinguish Earth life from Mars life by sequencing its DNA, as we can even tell which lab a strain of anthrax comes from
That humans on the surface can explore Mars much more quickly than any robot and do things in minutes that would take years for our robots

His followers are ready to be convinced. But these arguments are actually rather easy to demolish. I will explain how in this book. But before we get there, you might like to have a try at debunking them yourself. Here are a few questions to ask yourself. You may be surrprised at the answers when I get to them..

Try other analogies instead of sharks and lions, for the invasive species. Also - do we have invasive microbes on Earth?
When was the last asteroid impact on Earth large enough to send material all the way to Mars, through our thick atmosphere, exiting it at escape velocity? Compare this with the journey in a human occupied spacecraft. Which lifeforms could get there from an impact here? Could photosynthetic life?
What percentage of Earth microbes have had their DNA sequenced? If we find life on Mars, and have a portable DNA sequencer and it matches Earth life, great, we know it is introduced. But if we are unable to extract DNA or don't have a sequencer to hand, or the sequence doesn't match any of our well studied microbes, how do wet prove that it is native life from Mars, if Mars already has Earth life in all its habitats?
What would it be like to explore Mars robotically with hundreds or thousands of gigabytes of images building up a detailed 3D virtual landscape streamed back every day, and robots far more mobile and autonomous, traveling at tens of kilometers an hour with broadband communications back to Earth? We will probably have these capabilities by the mid 2020s. Compare with the way we explore the ocean depths.

If you have already been persuaded by his arguments, you may be interested and surprised at some of the things you learn from this book. It may help you to understand why so many scientists say that we should continue to protect Mars. However there is a lot of variety in views about what we need to do to protect it. NASA's planetary protection office and the Planetary society both see irreversible contamination by Earth life as inevitable after a human landing, if there are habitats for life there.

NASA's focus is on pproach is to keep Earth life away from the most sensitive areas on Mars for long enough to make scientific discoveries. The Planeteray society has a similar approach, but think that we need to study Mars as much as possible from orbit before we irreversibly contaminate it. In this book I'll suggest that we shouldn't set a date for a human landing on Mars at present, but should explore it from Earth and from orbit, until we feel we have a reasonable understanding of whether there are habitats there, and what the effect would be of landing humans on the planet, and leave any decisions about what to do next to the future.

Science fiction projections of the future are a mix of things astonishingly far sighted like the early stories about television before it was invented, and things that now seem bizarrely dated, such as Asimov's early stories about a huge supercomputer Multivac made of vacuum tubes, in one story described as filling Washington DC, and accessed by terminals world wide. In one of his stories "All the Troubles of the World" (1958), he describes it as "the giant computer that had grown in fifty years until its various ramifications had filled Washington, D.C. to the suburbs and had reached out tendrils into every city and town on Earth". It made sense at the time as that is how all computing was done, by communicating with huge "main frame" computers maintained by a team of technicians. That was still the situation through to the 1970s. If you wanted a portable calculator, you used a slide rule. So it's not surprising that in the first story to feature "faster than light" travel in science fiction, way back in 1938, the year before the first fully programmable electronic computer the Z3, John Campbell has explorers using slide rules to navigate spaceships that travel faster than light. (Full text). And of course, before the invention of colour TV, movie and TV programs had futuristic spaceships with the pilots staring at green monochrome displays on bulky cathode ray type monitors. Arthur C. Clarke in one of his best early short stories, not before the lunar landing, describes the Moon covered with fine dust so deep that rovers could sink into it without trace. All the early stories had oceans on Venus, and Mercury with one face permanently facing the sun. Early stories are a mix of far future technologies we don't have yet with what we now see as retro future ideas such as explorers using slide rules in spaceships that travel faster than light. (Full text)..

In one of his stories "All the Troubles of the World" (1958), he describes it as "the giant computer that had grown in fifty years until its various ramifications had filled Washington, D.C. to the suburbs and had reached out tendrils into every city and town on Earth".

, with possibly vast lunar caves and millions of tons of ice at the poles, with 24/7 sunlight nearly all year round

, Mercury, smaller asteroids and Callisto, and other places that we may be able to explore with no planetary protection issues depending on future discoveries such as the clouds of Venus, and only a small chance of issues for Mars' mooons Phobos and Deimos.

NASA's planetary protection officer Cassie Conley says that somehow we are going to find a way to land humans on Mars consistent with planetary protection. NASA's approach is to keep Earth life away from the most sensitive areas on Mars for long enough to make scientific discoveries, but based on the assumption that contamination is inevitable once you have humans there, and if there are habitats for Earth life on Mars. The Planeteray society has a similar approach, but think that we need to study Mars as much as possible from orbit before we irreversibly contaminate it.

My own very strong opinion which I present in this book is that we shouldn't just land humans on Mars as soon as we have the capability, and that our resources for Mars exploration are better used to hugely increase the pace with which we can search for life there robotically, and with humans in orbit, while the planet is still pristine. I think our future decisions should depend on what we find out as we do that. And meanwhile there are plenty of other places for humans to explore, in situ, and also to explore ideas of space settlement, including a return to the Moon, which has turned out to be far more interesting than expected.

If you find clear proof of life there - biosignatures, or even see the microbes swimming, and don't find DNA or the DNA doesn't match a known Earth species - would that count as a proof of native Mars life?

Science fiction projections of the future are a mix of things astonishingly far sighted like the early stories about television before it was invented, and things that now seem bizarrely dated, such as Asimov's early stories about Multivac made of vacuum tubes, in one of his stories "All the Troubles of the World" he describes it as " the giant computer that had grown in fifty years until its various ramifications had filled Washington, D.C. to the suburbs and had reached out tendrils into every city and town on Earth" , John Campbell with explorers using slide rules in spaceships that travel faster than light. (Full text)., and movie and TV programs with futuristic spaceships with the pilots staring at green monochrome displays on bulky cathode ray type monitors.Arthur C. Clarke in one of his best early short stories, not before the lunar landing, describes the Moon covered with fine dust so deep that rovers could sink into it without trace, and of course all the early stories had oceans on Venus, and Mercury with one face permanently facing the sun. The Mars trilogy and Mars colonization stories are bound to seem similar to future readers - a mix of the astonishingly prescient with the bizarrely out of date and just plain wrong.

Science fiction projections of the future are a mix of the far sighted like the early stories about television before it was invented, and things that now seem bizarrely dated, such as stories about explorers using slide rules in spaceships that travel faster than light. (Full text. Arthur C. Clarke in one of his best early short stories, not before the lunar landing, describes the Moon covered with dust so deep that rovers could sink into it without trace, and all the early stories had oceans on Venus, and Mercury with one face permanently facing the sun. The Mars trilogy and Mars colonization stories are likely to be similar to future readers - a mix of the astonishingly prescient with the bizarrely out of date and just plain wrong.

, John Campbell with explorers using slide rules in spaceships that travel faster than light. (Full text)., and movie and TV programs with futuristic spaceships with the pilots staring at green monochrome displays on bulky cathode ray type monitors.Arthur C. Clarke in one of his best early short stories, not before the lunar landing, describes the Moon covered with fine dust so deep that rovers could sink into it without trace, and of course all the early stories had oceans on Venus, and Mercury with one face permanently facing the sun. The Mars trilogy and Mars colonization stories are bound to seem similar to future readers - a mix of the astonishingly prescient with the bizarrely out of date and just plain wrong.

and the authors of the academic papers and workshop reports. But how can they involve the general public in these discussions, when it is so often not taken seriously at all, even by careful science reporters?

This is a detail from a screen shot from Star Trek Next Generation Season 5 Episode 23 I Borg (no particular reason, just happened to be watching it at the time I wrote this)

This is just a guess, but I wondered if it is possible that they were motivated partly by the Safe on Mars report in 2002 (which is cited by the decadal survey). This recommended a sample return from Mars to check to see if there are any biological hazards for humans on the surface. This is a 2010 animation showing how a sample return from Mars might have been done with 2010 era technology (they show it returned to the space shuttle).

<a href="https://youtu.be/Tv5_o69XuEs"> <img src="Touch_Mars_videos/video17msr.jpg" width="560" height="315"><br> (click to watch on YouTube)</a>

If so, it's interesting to note that Safe on Mars recommended a sample return only because at the time they wrote the report, there were no instruments sensitive enough to do a good search in situ, in their view. They say:

As stated above, there are currently no measurement techniques or capabilities available for such in situ testing. If such capabilities were to become available, one advantage is that the experiment would not be limited by the small amount of material that a Mars sample return mission would provide. What is more, with the use of rovers, an in situ experiment could be conducted over a wide range of locations.
(Page 41 of Safe on Mars)

So, actually, when you read it in detail, it's a similar recommendation to the one by the astrobiologists.

Well, now, these capabilities are available. Safe on Mars was written just two years after completion of the first draft of the human genome, completion of the three billion dollar human genome project in 2000

Some of the equipment used to sequence the human genome for the first time as part of a three billion dollar project, first incomplete draft released in 2000.

Now Oxford Nanopore markets the Minion, a gene sequencer on a USB stick, which can do the same thing!

Image from Smithonian magazine announcement of the minION before it was in production. Now it is widely used.

The advance in technology in the last 16 years in this field has been just incredible.

SETG which is currently at technological readiness level 4. They have all the components in place, but with some steps still done manually. It combines together two commercial devices - the minION for DNA sequencing with SimplePrep X1 for DNA extraction.

SETG consists of these two commercially available components for DNA sequencing which will be combined together to create a completely automated end to end DNA analysis system that can be sent to Mars to extract DNA and sequence it. This is a search to test for the possibility of life on Mars that is related to Earth life because of transfer of life from one planet to the other (or to both from a third souce such as Ceres) in the past. If there is any life there related to us, as distant cousins, based on DNA, then we can sequence it "in situ" and send the sequence back to Earth. This would have been inconceivable with the technology of only 16 years ago. Techy details and source paper for this image here.

Man othery instruments that were huge laboratory filling machines have now been miniaturized and a fair number also tested in space simulation conditions, and could easily be sent to Mars. These include electron microscopes, ultra sensitive biosignature detectors able to detect a single amino acid in a sample, and updated versions of the Viking Labeled release using chirality to eliminate false positives. Our instruments also include the exquisitely sensitive electrophoresis "lab on a chip" methods mentioned by Bada et al. Another new idea is the Solid3 approach of using polyclonal antibodies - which can detect, not just the organics you find in animal bodies, but a wide range of organics, again with exquisite sensitivity, in a "lab on a chip".

Why we can't prove that Mars life is safe for Earth

You may be convinced already by the examples of invasive species on Earth including invasive microbes. Do we want to find out if Mars life could be invasive and problematical species if introduced to Earth? But let's look at this in a bit more detail.

The main concern is not so much the effect on humans, though it’s not impossible that they could affect us. Joshua Lederberg - Wikipedia put it like this (he was a Nobel winning microbiologist, and microbe geneticist, and closely involved in early searches for life on Mars)

"If Martian microorganisms ever make it here, will they be totally mystified and defeated by terrestrial metabolism, perhaps even before they challenge immune defenses? Or will they have a field day in light of our own total naivete in dealing with their “aggressins”?

That’s in his "Paradoxes of the Host-Parasite Relationship" (he also gives an interesting analogy there with symbiosis with mitochondria)

Also

"Whether a microorganism from Mars exists and could attack us is more conjectural. If so, it might be a zoonosis to beat all others.

"On the one hand, how could microbes from Mars be pathogenic for hosts on Earth when so many subtle adaptations are needed for any new organisms to come into a host and cause disease? On the other hand, microorganisms make little besides proteins and carbohydrates, and the human or other mammalian immune systems typically respond to peptides or carbohydrates produced by invading pathogens. Thus, although the hypothetical parasite from Mars is not adapted to live in a host from Earth, our immune systems are not equipped to cope with totally alien parasites: a conceptual impasse."

(in Parasites Face a Perpetual Dilemma)

So, it’s not impossible that Martian microbes just colonize our bodies, and our bodies don’t realize they have to put up any defenses at all, because they don’t recognize it as life. Our immune system and defenses are keyed to various chemicals produced by Earth life, and it’s possible that Mars life simply doesn’t produce those chemicals. It might be rather like the way an artificial hip or heart replacement doesn’t get rejected from our bodies.

Carl Woese was another microbiologist who was concerned about a Mars sample return. He wrote in a private communication to Barry DiGregorio:

"I consider it a very adventuristic assumption that Earth is safe from Martian organisms. Obviously we know too little about life on Mars (even whether it exists) to make such assumptions. These are hand waving arguments whose only purpose is to rationalize the technological feats these people wish to accomplish. It appears that those making the case for sample return have not even considered organisms that would change the global organismal balance once they took hold - and what that would lead to is totally unpredictable. Indeed I get the feeling that those making the argument for sample return equate lack of knowledge (that it is unsafe) with lack of danger. This whole argument brings to mind the attitudes in NASA that Feynman wrote about in his book; Try it and if it doesn't work, then fix it. In this case your couldn't fix it if it didn't work ."

Not just us. Crops, sea, Environment of Earth

But it’s not just us. Our crops, the sea, animals, the environment of Earth generally, any could be affected by microbes returned from Mars with novel capabilities and perhaps totally different biology inside. For instance, what if they out compete photosynthetic life in the sea? And what if they are inedible to sea creatures, or they produce chemicals that poison them - not because they are adapted to harm us, but just because their chemistry is so different from ours? They can harm by competing, by being poisonous to us when eaten by unsuspecting Earth life, or just by altering habitats in ways that Earth life doesn’t find congenial to it.

Quarantine doesn’t work either. We can’t put everything that it could harm into the quarantine facility - and the effects could be delayed too. The latency period of leprosy is several decades. And if it’s microbes competing with microbes here, they may take up capabilities from Earth life via horizontal gene transfer (if related) or they may evolve to adapt to Earth conditions, or just meet some trigger that changes their behaviour. Again we can’t test for all that in a quarantine facility. It’s possible to quarantine against a known lifeform, but not when we don’t know what we are quarantining against and what its capabilities are.

As for putting humans in a quarantine facility - what do you do if the humans get ill? There is no way you’d just leave them in there to die, on the remote chance that it’s because of some microbe from Mars. It doesn’t prove it’s safe anyway, all it proves is that some humans were not affected when in a facility with the sample for a short period of time. It doesn’t even prove that it is safe for all humans, or that it won’t affect those humans later on, and of course tells us nothing about effects on other lifeforms. It’s hard to know what astrobiologists at the time would have recommended for Apollo - as the regulations were published on the day of launch and never had peer review (would not be acceptable nowadays). But they didn’t know enough to take adequate precautions back then, even without the many lapses in the published procedures (such as opening the Apollo command module door and evacuating the crew to a dinghy bobbing on the open ocean, which must have let dust from the Moon into the ocean, worst possible place to contaminate).

I have two new suggestions here that could, just possibly, help resolve this. First, though, for those of you who are new to this, let's just summarize the way that it would be done according current ideas.

TO DO:

Present day life with different form of photosynthesis and comparison with synthetic life made in labs on Earth
Unlikely life on Mars has reached the exact same stage of evolution as us and could be either more evolved or less (even if microbial and lichens it could be more evolved or less evolved microbes)
How it is easy to argue that case both ways based on the different history of Mars
That the most vulnerable type of life we could find on present day Mars - early life - could go extinct maybe quite soon after contamination with Earth life

Perchlorates are poisonous to many lifeforms. However, perchlorates are less hazardous at the low temperatures on Mars, and some Haloarchaea are able to tolerate them in these conditions, and some of them can use them as a source of energy as well. For details see "Perchlorate and halophilic prokaryotes: implications for possible halophilic life on Mars. Microbiologists now know of many microbes able to metabolize perchlorate, producing oxygen as a byproduct.

Unexpected Diversity of Bacteria Capable of Carbon Monoxide Oxidation in a Coastal Marine Environment, and Contribution of the Roseobacter-Associated Clade to Total CO Oxidation

Humvee journey through the Arctic - contamination study

Suggestion for protection of Earth during sample return - ionizing radiation

, but Mars transfer requires a delta v 3.4 km/sec from LEO, similar to the delta v of LEO to translunar orbit of 3.02 km / sec

Using an ultrasound machine on the ISS, experimenters found that the heart is 9.4% more spherical in space.

Need to send robotic explorers like VAMP to the Venus clouds first

Limitations of the method

Pristine Mars

So why did they send a lander to Titan instead of Europa?

Mission to Enceladus geysers - and identical mission to Europa

Huge disconnect between astrobiologists and decision makers

Why we can't prove that Mars life is safe for Earth

Not just us. Crops, sea, Environment of Earth

Preface

Could we get a future news story: "Debate over Moldy Mars is a Tale of Human Missteps"?

Raising awareness - fossil optimists and early life enthusiasts

Value of humans in space - and fossil hunters on the Moon?

Human settlement and exploration - hugely positive or hugely negative - it all depends how it is done

Contents