The main problems for water on Mars are that
As for the RSLs, we know hardly anything still about how the water forms, and in what form it flows down the slopes. All we know is that there are hydrated perchlorates associated with it in some way- not even definitely located in the dark streaks though that seems likely but they don't have the resolution to distinguish the streaks spectroscopically from the surrounding sand. And they can only observe at 3 pm because of the mapping orbit, which is the driest time of day. So - can't say much yet about the water and its habitability or otherwise. It might be too cold and salty for Earth life, but there again it might not. Which is why we can't use Curiosity to investigate close up if there happen to be any RSLs it could reach. It could only safely observe them optically from a distance.
The perchlorates aren't a problem for many Earth microbes, though poisonous for humans of course. Some microbes even use it as a source of energy- there are microbes in the Atacama desert that use perchlorates as an energy source.
Some microbes and Antarctic and high altitude lichens can even grow and photosynthesize in Martian conditions without any water at all just using the night time humidity, in simulation experiments done by DLR.
In the Atacama desert you also get microbes living in micropores in salt pillars, where water condenses onto the sides of the pores, just enough for salty brine, although the humidity of the atmosphere is well below the 60% or so humidity life normally needs to live in salt deposits - right down to 30% you still get some brine pockets that microbes can use.
So there could be microhabitats of various kinds on Mars. Even also microhabitats created by life itself, life living in biofilms for instance making the location more habitable than it would be for a single microbe - that is common on Earth.
And of course, that's just using Earth life as analogues. Mars life would be adapted to the conditions there for billions of years. And may have a different biochemistry, not even based on DNA - who is to say for sure that water that is too cold for Earth life can't be in inhabited by Mars life, for instance? We think -20 C is about the limit for Earth life. With some controversial research suggesting it might go lower in some situations. What if Mars life, however, can live at well below -20 C?
The limit of -20C plus reasonable water activity levels is what is used for definition of special regions - places where Earth life could possibly flourish on Mars. The RSLs are potentially special regions as nobody knows enough to say if there are habitats for Earth life there. But that doesn't mean there is no possibility of Mars life at lower temperatures. For instance the water found by Curiosity indirectly, because it is so cold, is not a contamination concern for Earth microbes on Curiosity they think. But - it could still perhaps be habitable to microbes adapted to Mars. It would be worth looking to check.
Ionizing radiation is not an issue at all on Mars for life that is able to revive and replicate every year, indeed would be enough if they revive just once every few hundred thousand years. Many microbes can tolerate dormancy for thousands of years even on Mars surface. The ionizing radiation levels there are similar to the interior of the ISS as measured by Curiosity. There is no protection from solar storms, but though deadly for humans, there are many microbes that would hardly notice them. They have the remarkable ability to repair their DNA in real time within a few hours. And that is for microbes that evolved on Earth and probably got that capability as a byproduct of desiccation resistance, which has similar effects on DNA. Life evolved on Mars and living near the surface would surely have the same capability to repair the damaging effects of ionizing radiation and probably be better at it than Earth life.
The reason they used to think the ionizing radiation makes Mars sterile is because they thought it was only habitable every few million years, and life couldn't survive millions of years of dormancy in the ionizing radiation conditions on the surface. But that's not an issue for life well below the surface - and more recently - they found these potential surface habitats and it is not an issue for those either so long as the life there revives occasionally.
See also my articles on Science20: NASA Says Mars Mystery Solved - What Is It? - Three Mysteries About Recursive Slope Lineae
Why Are Hydrated Salts A Slam Dunk Case For Flowing Water On Mars? And What Next?
Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,...
- It may be "too salty" - not enough water available for life to use
- It may be too cold
- It may be present for only part of the day - e.g. only when it is too cold for life
As for the RSLs, we know hardly anything still about how the water forms, and in what form it flows down the slopes. All we know is that there are hydrated perchlorates associated with it in some way- not even definitely located in the dark streaks though that seems likely but they don't have the resolution to distinguish the streaks spectroscopically from the surrounding sand. And they can only observe at 3 pm because of the mapping orbit, which is the driest time of day. So - can't say much yet about the water and its habitability or otherwise. It might be too cold and salty for Earth life, but there again it might not. Which is why we can't use Curiosity to investigate close up if there happen to be any RSLs it could reach. It could only safely observe them optically from a distance.
The perchlorates aren't a problem for many Earth microbes, though poisonous for humans of course. Some microbes even use it as a source of energy- there are microbes in the Atacama desert that use perchlorates as an energy source.
Some microbes and Antarctic and high altitude lichens can even grow and photosynthesize in Martian conditions without any water at all just using the night time humidity, in simulation experiments done by DLR.
In the Atacama desert you also get microbes living in micropores in salt pillars, where water condenses onto the sides of the pores, just enough for salty brine, although the humidity of the atmosphere is well below the 60% or so humidity life normally needs to live in salt deposits - right down to 30% you still get some brine pockets that microbes can use.
So there could be microhabitats of various kinds on Mars. Even also microhabitats created by life itself, life living in biofilms for instance making the location more habitable than it would be for a single microbe - that is common on Earth.
And of course, that's just using Earth life as analogues. Mars life would be adapted to the conditions there for billions of years. And may have a different biochemistry, not even based on DNA - who is to say for sure that water that is too cold for Earth life can't be in inhabited by Mars life, for instance? We think -20 C is about the limit for Earth life. With some controversial research suggesting it might go lower in some situations. What if Mars life, however, can live at well below -20 C?
The limit of -20C plus reasonable water activity levels is what is used for definition of special regions - places where Earth life could possibly flourish on Mars. The RSLs are potentially special regions as nobody knows enough to say if there are habitats for Earth life there. But that doesn't mean there is no possibility of Mars life at lower temperatures. For instance the water found by Curiosity indirectly, because it is so cold, is not a contamination concern for Earth microbes on Curiosity they think. But - it could still perhaps be habitable to microbes adapted to Mars. It would be worth looking to check.
Ionizing radiation is not an issue at all on Mars for life that is able to revive and replicate every year, indeed would be enough if they revive just once every few hundred thousand years. Many microbes can tolerate dormancy for thousands of years even on Mars surface. The ionizing radiation levels there are similar to the interior of the ISS as measured by Curiosity. There is no protection from solar storms, but though deadly for humans, there are many microbes that would hardly notice them. They have the remarkable ability to repair their DNA in real time within a few hours. And that is for microbes that evolved on Earth and probably got that capability as a byproduct of desiccation resistance, which has similar effects on DNA. Life evolved on Mars and living near the surface would surely have the same capability to repair the damaging effects of ionizing radiation and probably be better at it than Earth life.
The reason they used to think the ionizing radiation makes Mars sterile is because they thought it was only habitable every few million years, and life couldn't survive millions of years of dormancy in the ionizing radiation conditions on the surface. But that's not an issue for life well below the surface - and more recently - they found these potential surface habitats and it is not an issue for those either so long as the life there revives occasionally.
See also my articles on Science20: NASA Says Mars Mystery Solved - What Is It? - Three Mysteries About Recursive Slope Lineae
Why Are Hydrated Salts A Slam Dunk Case For Flowing Water On Mars? And What Next?
Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,...
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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