Okay mine isn’t an impressive geological feature like Olympus Mons or Valles Marineres. For me, it’s a rather unremarkable seeming crater, Richardson crater near the south pole. Let me explain why.

First this shows where it is. It is close to the south pole - this is an elevation map and I’ve trimmed it down to the southern hemisphere. You can see Olympus Mons as the obvious large mountain just right of middle, and Hellas Basin as the big depression middle left. Richardson crater is about half way between them and much further south.

Here is a close up - see all those ripples of sand dunes on the crater floor?

Link to this location on Google Mars

Well it’s not the ripples themselves that are of special interest, Mars is covered in many sand dune fields like that planet wide - but little dark spots that form on them which you can see if you look really closely from orbit.

Well, would you know, it is a possible habitat for life and it is quite possible that Earth life could reproduce there. That’s so surprising I know, as one of the coldest places on Mars. And it gets hardly any attention in Mars news stories for some reason. Lots of discussion of the Warm Seasonal Flows, but this one is only mentioned in very specialist papers by Mars researchers who specialize in the study of possible habitats on Mars. I don’t know why nobody else makes much of it.

First, early in the year, you get dry ice geysers - which we can’t image directly, but see the dark patches that form as a result and are pretty sure this is what happens:

So that would be cool enough, to be able to observe them, video them and study them close up. I hope the rover would be equipped with the capability to take real time video. Those are widely known and many scientists would tell you how great it would be to look at them up close.

But most exciting is what happens later in the year. It has these “flow like features” that grow during the year. The dark spots that you get in the aftermath of the geysers - you’d think would just sit there on the surface and gradually fade away ready to repeat the cycle next year. But no. Something very strange happens. Dark fingers being to form and creep down the surface as in this animation. Very quickly too (for Mars).

(animated version)
Flow-like features on Dunes in Richardson Crater, Mars. - detail. This flow moves approximately 39 meters in 26 days between the last two frames in the sequence

BTW it was hard to align these images exactly. I cut them out from the raw data, and aligned them by eye - unlike the RSLs there aren’t any widely shared images of them.

I’ve done my best to register them with each other but I couldn’t figure out a way to do it automatically, indeed, they are taken at slightly different angles also so there is no correct registration that puts each frame entirely in sync with the next one. So that’s why you may see some alignment shifts from one image to the next. It’s the best I can do. The general idea is clear enough.

All the models for these features, to date, involve some form of water.

That’s not as surprising as you might think. The same thing happens in Antarctica - if you have clear ice, then you get a layer of pure water half a meter below the ice. On Mars it would be about 5 - 10 cms below the surface and initially a few mms thick, and build up to 1–2 cms in thickness as the season progresses. The amazing thing is it would be fresh water at 0 C. That might seem rather chilly to you - but for many microbes it would be like a paradise on Mars.

The thing is any water on Mars exposed to the surface would evaporate quickly, so quickly that there would be none left. If ice melts there, it turns directly to water vapour because the atmosphere is a laboratory vacuum, it’s so thin.

But - water beneath a layer of transparent ice - that’s a different matter. The water is trapped by the ice so stays liquid. And what’s more, if they model it assuming clear ice like the ice in Antarctica they find that the ice there gets enough heat from the sun in the day to keep it liquid through the night to the next day so the layer can actually grow from one day to the next (ice is an excellent insulator).

The models are pretty clear. If Mars has transparent ice like the ice in Antarctica, then it should have layers of liquid fresh water about half a meter below the surface and a couple of cms thick in late spring to summer in this region.

The only question here is whether clear ice forms on Mars in Mars conditions. We can’t tell that really from models, the only way is to go there and find out for ourselves.

Blue wall of an Iceberg on Jökulsárlón, Iceland. On the Earth, Blue ice like this forms as a result of air bubbles squeezed out of glacier ice. This has the right optical and thermal properties to act as a solid state greenhouse, trapping a layer of liquid water that forms 0.1 to 1 meters below the surface. In Möhlmann's model, if ice with similar optical and thermal properties forms on Mars, it could form a layer of liquid water centimeters to decimeters thick, which would form 5 - 10 cms below the surface.

In his model, first the ice forms a translucent layer - then as summer approaches, the solid state greenhouse effect raises the temperature of a layer below the surface to 0°C, so melting it. This is a process familiar on the Earth for instance in Antarctica. On Earth, in similar conditions, the surface ice remains frozen, but a layer of liquid water forms from 0.1 to 1 meters below the surface. It forms preferentially in "blue ice".

On Mars, in his model, the melting layer is 5 to 10 cms below the surface. The liquid water layer starts off millimeters thick in their model, and can develop to be centimeters thick as the season progresses. The effect of the warming is cumulative over successive sols. Once formed, the liquid layer can persist overnight. Subsurface liquid water layers like this can form with surface temperatures as low as -56°C.

If the ice covers a heat absorbing layer at the right depth, the melted layer can form more rapidly, within a single sol, and can evolve to be tens of centimeters in thickness. In their model this starts as fresh water, insulated from the surface conditions by the overlaying ice layers - and then mixes with any salts to produce salty brines which would then flow beyond the edges to form the extending dark edges of the flow like features.

Later in the year, pressure can build up and cause formation of mini water geysers which may possibly explain the "white collars" that form around the flow like features towards the end of the season - in their model this is the result of liquid water erupting in mini water geysers and then freezing as white pure water ice

This provides:

• A way for pure water to be present on Mars, and to stay liquid under pressure, insulated from the surface conditions.
• 5 to 10 cms below the surface, trapped by the ice above it
• Depending on conditions, the liquid layer is at least centimeters in thickness, and could be tens of centimeters in thickness.
• Initially of fresh water, at around 0°C.

If salt grains are present in the ice, then this gives conditions for brines to form, which would increase the melt volume and the duration of the melting. The brines then flow down the slope and extend the dark patch formed by the debris from the Geyser, so creating the extensions of the flow like features.

They mention a couple of caveats for their model, because the surface conditions on Mars at these locations is unknown. First it requires conditions for bare and optically transparent ice fields on Mars translucent to depths of several centimeters, and it's an open question whether this can happen, but there is nothing to rule it out either. Then, the other open question is whether their assumption of low thermal conductivity of the ice, preventing escape of the heat to the surface, is valid on Mars.

The process works with blue ice on Earth - but we can't say yet what forms the ice actually takes in these Martian conditions.

This solid state greenhouse effect process favours equator facing slopes. Also, somewhat paradoxically, it favours higher latitudes, close to the poles, over lower latitudes, because it needs conditions where surface ice can form on Mars to thicknesses of tens of centimeters. (The examples at Richardson crater are at latitude -72°, longitude 179.4°, so only 18° from the south pole.

There is no in situ data yet for these locations, of course, to test the hypothesis. Though some of the predictions for their model could be confirmed by satellite observations.

Interfacial liquid layers model

Another model for these southern hemisphere features involves ULI water (undercooled liquid water) which forms as a thin layer over surfaces and can melt at well below the usual melting point of ice. In Mohlmann's sandwich model, then the interfacial water layer forms on the surfaces of solar heated grains in the ice, which then flows together down the slope. Calculations of downward flow of water shows that several litres a day of water could be supplied to the seepage flows in this way.

The idea then is that this ULI water would be the water source for liquid brines which then flow down the surface to form the features.

That would still be interesting as you end up having flowing liquid water on Mars, several litres a day what’s more.

Those are the only two models so far. So it does seem very likely that there is liquid water here, and even with the interfacial liquid layers, the water starts off as fresh water beneath the ice, or possibly salty (in either model) if there are salt grains in the ice for the water to pick up.

It would be great if somehow we could land a rover near there to travel over to these flows and study them close up with in situ life detection instruments. Though it would need to be sterilized very carefully, we must be absolutely sure that we can’t introduce Earth life there or it would destroy much of the science value for exobiology and might even make whatever is there extinct before we can study it if there is life there.

To see how whatever there is there could be made extinct, easily, think of the possibility of some early form of life, e.g. without proteins or DNA, based on RNA only (one theory, the RNA world theory). All earlier forms of life seem to have been made extinct by DNA life on Earth, but they might still exist on Mars. If so they would be extremely vulnerable to introduced Earth life. This is just one scenario according to which introduced Earth life could cause problems or even completely destroy much of the exobiology science value of Mars.

Note that there are flow like features in the Northern hemisphere, but these form at much colder temperatures for some reason, around -90°C - the two hemispheres on Mars have a very different climate. The northern hemisphere has shorter warmer winters (due to Mars’s eccentric orbit), and a lower elevation, but the flow like features there form at times when the surface temperatures are lower than in Richardson crater. There are several different mechanisms for the northern hemisphere flow like features, not all the models for those involve liquid water, and the ones that do involve very cold water. So the Richardson crater ones are the surest bet, seems to me, for a habitable flow like feature.

There are many other seasonal features on Mars but most are caused by dust, wind, or dry ice. The Warm Seasonal Flows or RSLs are the best known, of the ones that may provide habitats for life, indeed there is indirect detection of water flowing there through hydrated salts, those also seem a pretty sure bet for liquid brine but the question there is, is the brine warm enough, for life, and if it is warm enough is it too salty or is it fresh enough for life?

In the case of the Richardson Crater flow like features - especially if they are indeed cms thick layers below clear ice - they will definitely 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 water that then picks up salts on its way out.

This is just one of many habitats suggested on the Mars surface. But I like to draw attention to it because it is one of the least publicized, yet in some ways most interesting potential habitats because of the potential for fresh water at 0 C. As far as I know it is the only surface habitat so far that has the potential to be so warm and also to have fresh water. For some of the others, see

• Warm Seasonal flows (Recurrent Slope Lineae)
• Sun warmed dust grains embedded in ice
• Flow like features (this one)
• Life able to take up water from the 100% night time humidity of the Mars atmosphere
• Deliquescing salts taking up moisture from the Mars atmosphere
• Advancing sand dunes bioreactor
• Droplets of liquid water on salt / ice interfaces
• Shallow interfacial layers a few molecules thick

NEED FOR ROBOTIC EXPLORATION FIRST

This is just one of many possible locations for life on Mars. But one of the most promising I think since it is habitable for Earth life. 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. Imagine if you could learn about life on a planet or in the ocean of an icy moon around another star? Even if it was just extraterrestrial microbes or lichens, imagine how exciting that discovery would be? Well Mars, Europa and Enceladus may be like exoplanets and exomoons in our own solar system, they may be as interesting as that. We don't know until we study them close up.

It's 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.

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.

WHAT WE COULD LEARN - SOME EXAMPLES

• Early life, e.g. tiny RNA world microbes without DNA or proteins
• Life based on different principles. 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
• Life with a capability Earth life doesn't have, e.g. a new form of photosynthesis. We have three ways of doing photosynthesis on Earth - broadly speaking. Plants and some microbes produce oxygen from water, some microbes produce sulfur from hydrogen sulfide (sulfur bacteria), and some use the light to power a "proton pump" producing ATP directly from hydrogen (purple bacteria such as the haloarchaea, using bacteriorhodopsin similar to the rhodopsin in our eyes, instead of chlorophyl). So what if life on Mars has a fourth way of doing photosynthesis. Though not so totally revolutionary as an early RNA lifeform or a different biochemistry, it would still be an extraordinary discovery and major event in biology. Those are just examples. We can't know in advance what we will find but it does have potential to be revolutionary.
• If similar to Earth life in most respects, we can learn from the differences, how it evolved in such a different environment, since last transfer from Earth, surely at least tens of millions of years ago. We can also test the theory of panspermia, find out in practice how easy it is for life to be transferred to another planet.
• If there is no life, we learn a lot about what happens on a world with organics and all the ingredients for life but no life. We can also learn to distinguish between the effects of life and non life on a planet - on Earth it's impossible to study uninhabited habitats, except for a very short time after a volcanic eruption. Life appears rapidly. On Mars, we might have the opportunity to study uninhabited habitats on a planet that hasn't been inhabited for billions of years. This could help us to understand exoplanets and the origin of life and maybe find out that life is harder to evolve than we thought. It can also help to disentangle effects of life and non life processes on Earth.

All possibilities here are of exceptional interest for biology. If there are habitats for life at all on Mars, whether inhabited or uninhabited, then biologists world wide will want to study them as they are now, and the results in the best case could be revolutionary for biology.

Here is a list of some of them, for the cites see my Candidate lifeforms for Mars in my Places on Mars to Look for Microbes, Lichens, ...:

• Chroococcidiopsis - UV and radioresistant, and can form a single species ecosystem. It needs no other forms of life, and only requires CO2, sunlight and trace elements to survive.
• Halobacteria - UV and radioresistant, photosynthetic (using hydrogen directly - proton pumps, doesn't generate oxygen or sulfur), can form single species ecosystems, and highly salt tolerant. Some are tolerant of perchlorates and even use them as an energy source, examples include Haloferax mediterranei, Haloferax denitrificans, Haloferax gibbonsii, Haloarcula marismortui, and Haloarcula vallismortis
• Some species of Carnobacterium extracted from permafrost layers on Earth which are able to grow in Mars simulation chambers in conditions of low atmospheric pressure, low temperature and CO2 dominated atmosphere as for Mars.
• Geobacter metallireducens - it uses Fe(III) as the sole electron acceptor, and can use organic compounds, molecular hydrogen, or elemental sulfur as the electron donor.
• Alkalilimnicola ehrlichii MLHE-1 (Euryarchaeota) - able to use CO in Mars simulation conditions, in salty brine with low water potentials (−19 MPa), in temperature within range for the RSL, oxygen free with nitrate, and unaffected by magnesium perchlorate and low atmospheric pressure (10 mbar). Another candidate, Halorubrum str. BV (Proteobacteria) could use the CO with a water potential of −39.6 MPa
• black molds The microcolonial fungi, Cryomyces antarcticus (an extremophile fungi, one of several from Antarctic dry deserts) and Knufia perforans, adapted and recovered metabolic activity during exposure to a simulated Mars environment for 7 days using only night time humidity of the air; no chemical signs of stress.
• black yeast Exophiala jeanselmei, also adapted and recovered metabolic activity during exposure to a simulated Mars environment for 7 days using only night time humidity of the air; no chemical signs of stress.
• Methanogens such as Methanosarcina barkeri[200] - only require CO2, hydrogen and trace elements. The hydrogen could come from geothermal sources, volcanic action or action of water on basalt.
• Lichens such as Xanthoria elegans, Pleopsidium chlorophanum, and Circinaria gyrosa - some of these are able to metabolize and photosynthesize slowly in Mars simulation chambers using just the night time humidity, and have been shown to be able to survive Mars surface conditions such as the UV in Mars simulation experiments.

Most of these candidates, apart from the lichens, are single cell microbes (or microbial films). The closest Mars analogue habitats on Earth such as the hyper arid core of the Atacama desert are inhabited by microbes, with no multicellular life. So even if multicellular life evolved on Mars, it seems that most life on Mars is likely to be microbial.

For more about the value of Mars for biology and implications of sending humans there, see

• Does Elon Musk's Plan Violate The Outer Space Treaty - Planetary Protection For Mars After Human Crashes
• Wait, Let's Not Rush To Be Multiplanetary Or Interstellar - A Comment On Elon Musk's Vision

OVER PROTECTION OF MARS THESIS

Robert Zubrin has said he thinks that there may well be habitats for Earth life on Mars, but that if so, those habitats have the same life as Earth so there is no problem contaminating it with Earth life. The astrobiologist Dirk Schulze-Makuch and the astronomer Alberto G. Fairén published an article "The over protection of Mars" also putting forward this view which got a lot of publicity. Few people have read the response "Appropriate protection of Mars" refuting it, by the current and previous planetary protection officers. Both papers were published in Nature. They are behind firewalls but you can read a summary of them both in The Overprotection of Mars? - Astrobiology Magazine

The astrobiologists who wrote "Over protection of Mars" think that life on Mars is going to be pretty much identical to Earth life in all respects. But that is a minority view. It could equally well be very different indeed. Their reasoning is that Earth and Mars have shared a lot of material via meteorites. But that only happens after really huge impacts on Earth like the Chicxulub meteorite 66 million years ago.

To get to Mars a microbe in the warm tropical sea which this asteroid hit will have to survive first the shock of impact. Then it has to survive 100 years minimum in space (when first pieces get to Mars) in the extreme cold of space, vacuum conditions and solar storms and cosmic radaiation. Then it has to survive the shock of impact on Mars, then it has to find a habitat once there, and it has to be sufficiently pre-adapted to that habitat to survive and reproduce. It also has to be capable of forming a single species ecosystem - or else, to be able to survive in collaboration with whatever microbes are there already.

When I was young, in the sixties and seventies, most scientists thought panspermia was a daft idea. The rather eccentric scientists Fred Hoyle and Chandra Wickramasinghe put it forward and no-one else believed them. Now it's gone the other way. People speak about panspermia as if it has been proven. But though we have found some remarkable extremophiles, that just possibly might survive such a journey, it still remains just a theory. We don't yet have a single example of a microbe that has been transferred between planets.

It might never have happened. It might have happened but only in the early solar system in the first few hundred million years after the Moon formed. Or it might be that it happened as recently as 66 million years ago.

Any life that got there 66 million years agp also has had all that time to evolve in the very different Martian conditions. It does now seem possible that some very remarkable polyextremophile microbes able to withstand, cold, vacuum, impact shock, radiation etc, could get there. Chrooccocidiopsis is a good candidate, a polyextremophile also forms single species ecosystems, anaerobe, survive almost anywhere on Earth.

However, it doesn't seem likely at all that e.g. any lichens have got from Earth to Mars in that way. Yet they could survive on Mars. Depending what types of habitats actually exist on Mars, there may be many other lifeforms that could survive on Mars and yet may have no chance to get there on a meteorite.

I think that for most astrobiologists, Dirk Schulze-Makuch and Alberto Fairén have presented a rather extraordinary hypothesis about Mars which would need to be proved. There would be bound to be at least some differences. And if we did find life there almost identical to Earth life, that itself would be so extraordinary we would want to study it carefully to find out how that happened. The last you'd want to do in that situation is to introduce lots of Earth microbes to confuse the situation.

And it is well possible that Mars has its own unique lifeforms. Even if some Earth life got there, it may well play nicely with whatever is there already. For instance a green algae such as Chroococcidiopsis might well play nicely with existing life on Mars. That would not mean that all Earth life is as congenial to life there.

IDEA THAT LIFE ADAPTED TO MARS COULD NOT BE VULNERABLE TO EARTH LIFE

Robert Zubrin says this frequently in his talks about colonizing Mars. But the idea just doesn't pan out if you look at it in any detail. First, any life on Mars may be driven extinct by Earth life. It doesn't follow at all that because it is adapted to Mars that it is not going to go extinct. The easiest way to see that is that is if it is some earlier form of life, such as RNA world life.

Perhaps some microbes like Chroococcidiopsis would not make early life extinct, after all it is a primary producer, it does not eat other lifeforms and the oxygen it produces as a byproduct would be no problem on Mars as it has a very oxygenated surface already with perchlorates in place of chlorides and even hydrogen peroxide - lifeforms that can withstand those won’t be bothered by a bit of oxygen.

But we don't have any early life left on Earth and our earliest life we do have is far too complex to have evolved in one go. So if it still exists on Mars, then it may be very vulnerable to whatever made it extinct on Earth.

Robert Zubrin gives the analogy of sharks out competing lions in their native habitat which is absurd. Sharks can’t even survive for minutes in the African savannah. But we have many microbes that can survive just fine on Mars if the suggested habitats exist. For a different analogy, rabbits and rats out compete wallabies, and many invasive plants out compete native plants. So it just depends which species you use for your analogy. We don't have problems with sharks competing with lions but we do have problems with rabbits competing with wallabies. Who is to say which is the right analogy for Mars? We just don't know until we find out more.

Also he has another argument that he brings up in all his Mars colonization talks - that it should be easy to tell whether life is from Mars or from Earth using the analogy of anthrax. Yes there are some lifeforms we have sequenced and would recognize on Mars. Anthrax is an example. But only 100,000 of one trillion microbe species, 0.00001% have had gene sequences published. It's not at all practical to have an "inventory" of every single microbial species on the spaceship.

So, no, we would not know if a microbe on Mars comes from Earth or Mars, so long as it shares an ancestor with Earth, even as long ago as well over three billion years ago, when the archaea first evolved. The Origins of Archaea and Bacteria

Also the archaea swap DNA fragments readily with each other through horizontal gene transfer (by Gene Transfer Agents). This is an ancient mechanism which works between the most distant most unrelated archaea. So if there is a common ancestor, even from 4 billion years ago, the chances are that after introducing Earth life you have a hybrid of Earth and Mars DNA for any life that is related to Earth life.

MYTH OF AUTOMATIC TERRAFORMING

This is the idea that if you add microbes to a planet, no matter what they are, that it will automatically turn into a second Earth or the closest to Earth that's possible for the planet. I call that the "myth of automatic terraforming". To see why that is not automatic, think of a future Earth too hot for life, a billion years into the future. It would just have extremophiles.

Just possibly there might be some biological way to do something about this to cool down that future Earth using microbes - but why would just adding a lot of microbes from present day Earth cool it down automatically? If it could sort itself out, it would have done it already. Mars may well have life already, and if so, it has not terraformed it, and why then would life from Earth terraform it if its own native life has not?

Adding life to a planet could push it in many different ways and there is no way of knowing if it would make it better or worse. The one thing it definitely does do though is to close off future options. After you've done that, you can never roll back, if you later find that one of the lifeforms you introduced is a major problem on the planet. Not with microbes. It is hard enough to roll back higher lifeforms like rabbits, cane toads, rats, Kudzu or Japaanese knotweed. Even camels are a problem in Australia since the continent is so huge. How could you roll back a problem microbe from a planet as large as the land area of Earth?

What will you do if you have introduced some problem microbe? Maybe you want to increase oxygen levels but you introduced aerobes that eat the oxygen? Maybe you want to increase methane levels but you accidentally introduced methanotropes that eat it? Maybe you introduced secondary consumers that eat the algae that you want to use to introduce oxygen. Many things could go wrong as a result of microbes you introduced by mistake.

As one simple example of how microbes introduced by mistake could mess things up quickly, some bacteria convert water to calcite, and if you introduce them by mistake, you might find that these microbes have converted all the underwater aquifers to cement. That's an example from Cassie Conley, current planetary protection officer for the USA - she is a microbiologist / astrobiologist.

Going to Mars Could Mess Up the Hunt for Alien Life

I think this is based originally on Lovelock’s Gaia hypothesis in its strong form, the idea that life makes planets more habitable for itself. The weak Gaia hypothesis that the Earth has many systems that work together to help keep it in a habitable state, mediated by life, is widely accepted. But the idea that such a system arises automatically on all terrestrial planets with life is not at all universally accepted. That’s the “strong Gaia hypothesis”. Some things about our own planet are puzzling, for instance, why did photosynthetic life evolve at just the right time to turn a CO2 into oxygen, to cool our planet to keep it habitable, instead of arising too soon, to make it too cold, or too late, leaving it too hot? Then in science fiction the strong Gaia hypothesis has been exaggerated to mythology, the idea that introducing life to a planet not only helps keep it habitable for that life, but that it also automatically makes it habitable for humans too. Why? Even if the strong Gaia hypothesis was true - well the way to make Mars the most habitable it could be for life would be for methanogens to evolve to convert all the atmosphere to methane, which is a strong greenhouse gas. That would make Mars nearly as warm as it could be, using natural methods, though if the strong Gaia hypothesis was true, then surely also the life would evolve to generate stronger and stronger greenhouse gases on Mars to keep it warm. That would make it more habitable, but not an environment humans could live in. I think few would subscribe to such a strong version of the Gaia hypothesis. But the idea that life would automatically make Mars Earth like is even more absurd than that one, I think.

Introducing Earth life to Mars would probably do nothing to make it more habitable, not without some long term plan, mega engineering, and careful selection of which lifeforms to introduce when. And it would probably need artificial greenhouse gases or large planet scale mirrors or both to remain warm enough long term. In a thousands of years project that then goes on and on, trillions of dollars a year keeping it habitable.

I think it is great to think about terraforming ideas, yes. It helps us learn a lot about our planet and exoplanets and Mars itself to do those thought experiments. But as for practical experiments, let’s start a lot smaller. We haven’t yet managed a closed system ecosystem the size of Biosphere II on Earth. Once we have very small closed system ecosystems on Earth, then we can try it in space also, for instance in the possibly vast lunar caves, maybe as large as an O’Neil cylinder, a hundred kilometers long and kilometers wide. Then we can work up to larger maybe city dome or Stanford Torus type ecosystems. Eventually we can try Terraforming and paraterraforming the Moon. Let’s leave off ideas to terraform planets until we know a bit more.

And - let’s keep Mars pristine for scienctific 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.

I fully understand how those who are keen on colonization of space want to land humans on Mars as soon as possible. They’ve been looking forward to this for decades some of them. 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 On Mars So Easily? A crash of a human occupied ship would be the end of planetary protection of Mars for science.

I think that our objective for humans to Mars should be humans to Mars orbit and possibly Phobos and Deimos, exploring the surface via telepresence. And as for our first experiments in biological closed systems, paraterraforming, commerce from space etc, I think all of those should be done on the Moon and in NEOs, leading later to exploration throughout the solar system. But the places of most interest for the search for life need to be protected indefinitely, until we know enough to make informed decisions about them. The top priorities there are Mars, Europa, Enceladus, and then there are others that need to be investigated before we know if they are vulnerable such as Ceres.

For more on this, see this section of my Case for Moon First (and following) wjocj may give pause for thought:

• Case For Moon First - Myth of automatic terraforming

For more about the flow like features habitat, and many other possible habitats on Mars, see my

(notice I put the Richardson flow-like features on the cover - for me, this is the most exciting feature of all on Mars for exobiology)

Places on Mars to look for Microbes, Lichens, ... Salty Seeps, Melt Water Under Clear Polar Ice, Ice Fumaroles, Dune Bioreactors, ...: Where early Mars lifeforms could survive to the present day,

It’s also available to read online for free at Places on Mars to Look for Microbes, Lichens, ... and the section on the Richardson flow-like features is here: Flow like features

See also my books:

"MOON FIRST Why Humans on Mars Right Now Are Bad for Science", available on kindle, and also to read for free online.

Case For Moon First: Gateway to Entire Solar System - Open Ended Exploration, Planetary Protection at its Heart - kindle edition or Read it online on my website (free).