Okay - you might think so - but - if you do the numbers, turns out it would be far far harder to spot than you'd expect because of cosmic radiation.
Most likely type of life is some kind of microbial life. And - the problem is cosmic radiation degradation. No bones. Might get stromatolite type formations - but they would be hard to recognize - the oldest stromatolites on Earth were highly controversial until they eventually found organics in them.
So what they are looking for are organics.
And - you might then look at something like, say, the oil rich shales of the USA Green River Formation with its estimated 480 billion cubic metres of oil shale - which formed over a relatively short time period, 2000 meters depth of organics formed over 5 million years - with its richest 1.8 meter deposit forming over 1000 years - and think - what if Mars has formations like that - would we not spot them?
But - look at the effects of cosmic radiation. It has almost negligible effect over a few years - and living organisms can survive for decades or longer in dormant state on the surface. But over millions of years it has a big effect, and over billions of years, the effect is absolutely huge.
It reduces the amount of organics a trillion fold every billion years approximately.
The effect of ionizing radiation on the preservation of amino acids on Mars =- take a look at the table from his paper
Shows the fraction that would be left after exposing amino acids to cosmic radiation for half a billion years (top curve), a billion years, and 3 billion years at various depths on Mars.
So - you can see - that surface deposits of organics are reduced by about a trillion fold after a billion years. After three billion years - they would be reduced a trillion trillion trillion fold.
It would reduce a deposit of 1000 tons down to a few milligrams if on the surface after a billion years - and if it was more like three billion years - even those few milligrams would vanish to almost nothing. You wouldn't even have micrograms left. Given that avogadro's number is 10^23 - you are down to the point where there might not be a single molecule left of your original deposit after 3 billion years.
Most of that escapes as volatiles such as CO2 and methane etc that evaporate into the atmosphere.
So - as a result it's a major challenge to find past life on Mars.
Of those 480 billion cubic metres of oil shale, then after a billion years you are left with 0.5 cubic meters, and after another billion years it is down to 0.001 cubic millimeters, and after another billion years down to probably not even any single molecules left of your deposit.
Well - maybe that's a bit of a simplified calculation if the deposit is 2000 meters deep - but there would be nothing at all left of the top layers of it. You'd have to dig deep - and then you might find those millions of tons of organics just a few meters below the surface if you look in just the right place - if Mars did ever have such rich deposits as that. But not likely on the surface.
And the other thing to bear in mind is - that Mars had a much shorter past than the Earth before it got too cold for life to flourish at least not in huge quantities any more. Just a few hundred million years. And for much of that it was cold probably, more like Arctic sea ice than the tropics. So far less productive - and also got half the light levels of Earth.
So instead of those thousands of meters of deposits - might well be that the layers of organics were just a few tens of cms thick originally.
And - we don't know for sure that photosynthesis developed on Mars early on - suppose it didn't - suppose it didn't develop until hundreds of millions of years later - by which time it was too late to create these thick deposits - then we need to check out hydrothermal vents (say) - might then be a major challenge just knowing where to look.
We have actually spotted deposits identified as likely to be the remains of hydrothermal vents on Mars - from orbit.
http://www.nasa.gov/images/conte...
And Opportunity also discovered possible hydrothermal vent materials at the rim of Endeavour crater. - but of course doesn't have the capability to drill or to search for life in the deposit.
If that's where we need to go to look for past life, will be at least a while before we go there. (You can't do everything at once, and also - some areas of Mars are far easier for our rovers to visit than other areas).
We need to look in the right place - and find deposits that - originally had lots of organics - and then were buried very quickly - like over a few million years at most. Then they need to stay buried undisturbed - the later floods on Mars could easily wash out all the organics, especially if they were in some soluble matrix, say salts.
Then - after spending those three billion or more years buried more than 10 meters below the surface - need to be exposed to the surface quickly within a few million years.
That's why it was so remarkable when Curiosity detected what seemed to be traces of early organics. It's not that sensitive to these things -not compared to ExoMars. Couldn't detect single molecule biosignatures.
But - this must have been quite a big deposit - and then exposed to the surface quickly - so that there were enough organics left for Curiosity to detect them.
Another thing that confuses the whole picture also - is that comets and meteorites also contain amino acids. And they also are often chiral - in pristine meteorites recovered almost immediately after they landed on the Earth - in Antarctica or in deserts - not likely to be contaminated with Earth organics - they often find a chiral excess rather like life - of one amino acid over another - and quite large excesses also.
However - distinguishable from ordinary Earth life as they tend to include amino acids not used by Earth life in its biochemistry. On Mars though detection of those amino acids would not let you tell if it was life or meteorites as of course Mars life could easily use different amino acids from Earth life.
So - even when they find biosignatures on Mars - assuming they do - is going to be a major detective puzzle to show that it is past life.
Some think that we are more likely to be able to detect present day life. The problem there is that the conditions are so harsh on Mars - that we probably are talking about just a few microbes here and there, similar to the Atacama desert, really hard to detect again. And - if we can't cultivate them either - then might be pretty hard to distinguish them.
Might spot them in microscopes. But we saw with Allan Hills 84001
that even if you spot microscopic structures that look like life - they can still be controversial.
These are too small for Earth life, smaller than the smallest possible modern DNA based cell. But just the right size for some earlier form of life that might have existed before Earth microbes. Perhaps they are Martian lifeforms. But the jury is out because they have inorganic explanations as well.
That could be a problem for both present day life on Mars and also ancient fossil life - if there are any fossils left for us to find.
However - does seem promising enough that we will find them eventually. Just need to hit it lucky and find a deeply buried, rapidly excavated ancient deposit still in relatively pristine state. Then might also detect complex organic compounds as well.
It also helps a lot if you can dig even a few meters below the surface.
ExoMars will be able to dig down 2 meters, which may not seem much but if you look at this graph again
It makes a huge difference. Even digging 1 meter makes a huge difference to your chance of finding billions of years old organics.
It does still have to be buried quickly - not much point digging two meters into a deposit that formed slowly over billions of years. And need to know where to dig. Not a stroll in the park :). But - if we keep looking we have a decent chance of finding good evidence of past life on Mars.
And we do have wind constantly excavating (that's what Curiosity is hoping to find, recent wind exposed ancient organics deposits) - and craters also excavated by meteorites. So - we do have a reasonable chance of finding the past life eventually.
And for present day life also - if we keep searching and use sufficiently sensitive detectors - able to detect a single organic molecule in a sample.
Oh, and there is another possible place to look for life. Deep underground, in the hydrosphere. Mars unlike Earth has a cryosphere on its surface, extending from the permafrost layer just a couple of cms below the surface, down for several kms. It's thought to be very dry for a long way down in the equatorial regions - but with some evidence of possible patches of trapped ice. Anyway - deep down it eventually gets hotter, just as on Earth - and eventually gets hot enough for ice to melt - and also - enough pressure there for water to be liquid. So - there might be, say, 100 meters maybe more depth of liquid water way down there - which might be an ideal habitat for life.
It's possible to drill down to it - are plans for unmanned landers that could drill all the way down through kms of rock using robotic moles - so maybe one day we'll get a chance to find out if there is life there. But - not the easiest target for an early search, obviously, for its depth - no matter how common or rare life turns out to be down there.
There may however be geothermal hot spots that bring liquid water closer to the surface trapped beneath layers much like the way oil gets trapped on the Earth. Also might be life in caves similarly maybe a cave that has access to a geological hot spot.
In short the main places to look are
I think we will find it eventually. But could be a long search. Shouldn't give up for instance if ExoMars fails to find it - though I think it does have a chance of finding past life on Mars.
Even if there was macroscopic Mars life, e.g. lichens, or multicellular life forms - it might take a while to find it - after all - hard enough to find on Earth - we have different challenges on Mars. No continental drift. But lots of floods, meteorite impacts - and all the cosmic radiation toughest of all.
There might be macrofossils also - e.g. stromatolites. But if so - we need to know what they look like, with some examples, before we can identify them. Enthusiasts point out loads of "life like" formations in the rocks. But you also get things that look like like that are formed by inorganic processes.
So until we know what we are looking for, we can't just go by appearances. If one of our rovers saw this on Mars I would imagine that many people would tweet saying it has to be life. But this is actually a "desert rose" from Earth - and a well known inorganic phenomenon you get in deserts.
For more about this see:
Where Should we Send our Rovers to Mars to Unravel Mystery of Origin of First Living Cells?
Most likely type of life is some kind of microbial life. And - the problem is cosmic radiation degradation. No bones. Might get stromatolite type formations - but they would be hard to recognize - the oldest stromatolites on Earth were highly controversial until they eventually found organics in them.
These are early stromatolites - but they only know that because of analysis of organic traces in the rocks. Were controversial for a long time. If we spot things like this on Mars - they might be stromatolites - but might just be rock formations formed in other ways.
So what they are looking for are organics.
And - you might then look at something like, say, the oil rich shales of the USA Green River Formation with its estimated 480 billion cubic metres of oil shale - which formed over a relatively short time period, 2000 meters depth of organics formed over 5 million years - with its richest 1.8 meter deposit forming over 1000 years - and think - what if Mars has formations like that - would we not spot them?
But - look at the effects of cosmic radiation. It has almost negligible effect over a few years - and living organisms can survive for decades or longer in dormant state on the surface. But over millions of years it has a big effect, and over billions of years, the effect is absolutely huge.
It reduces the amount of organics a trillion fold every billion years approximately.
The effect of ionizing radiation on the preservation of amino acids on Mars =- take a look at the table from his paper
Shows the fraction that would be left after exposing amino acids to cosmic radiation for half a billion years (top curve), a billion years, and 3 billion years at various depths on Mars.
So - you can see - that surface deposits of organics are reduced by about a trillion fold after a billion years. After three billion years - they would be reduced a trillion trillion trillion fold.
It would reduce a deposit of 1000 tons down to a few milligrams if on the surface after a billion years - and if it was more like three billion years - even those few milligrams would vanish to almost nothing. You wouldn't even have micrograms left. Given that avogadro's number is 10^23 - you are down to the point where there might not be a single molecule left of your original deposit after 3 billion years.
Most of that escapes as volatiles such as CO2 and methane etc that evaporate into the atmosphere.
So - as a result it's a major challenge to find past life on Mars.
Of those 480 billion cubic metres of oil shale, then after a billion years you are left with 0.5 cubic meters, and after another billion years it is down to 0.001 cubic millimeters, and after another billion years down to probably not even any single molecules left of your deposit.
Well - maybe that's a bit of a simplified calculation if the deposit is 2000 meters deep - but there would be nothing at all left of the top layers of it. You'd have to dig deep - and then you might find those millions of tons of organics just a few meters below the surface if you look in just the right place - if Mars did ever have such rich deposits as that. But not likely on the surface.
And the other thing to bear in mind is - that Mars had a much shorter past than the Earth before it got too cold for life to flourish at least not in huge quantities any more. Just a few hundred million years. And for much of that it was cold probably, more like Arctic sea ice than the tropics. So far less productive - and also got half the light levels of Earth.
So instead of those thousands of meters of deposits - might well be that the layers of organics were just a few tens of cms thick originally.
And - we don't know for sure that photosynthesis developed on Mars early on - suppose it didn't - suppose it didn't develop until hundreds of millions of years later - by which time it was too late to create these thick deposits - then we need to check out hydrothermal vents (say) - might then be a major challenge just knowing where to look.
We have actually spotted deposits identified as likely to be the remains of hydrothermal vents on Mars - from orbit.
http://www.nasa.gov/images/conte...
Volcanic cone in Nili Patera Caldera. The light coloured deposits marked with the arrows are hydrothermal vent deposits, which show that it must originally have been warm and wet in the ancient Noachian period.
And Opportunity also discovered possible hydrothermal vent materials at the rim of Endeavour crater. - but of course doesn't have the capability to drill or to search for life in the deposit.
If that's where we need to go to look for past life, will be at least a while before we go there. (You can't do everything at once, and also - some areas of Mars are far easier for our rovers to visit than other areas).
We need to look in the right place - and find deposits that - originally had lots of organics - and then were buried very quickly - like over a few million years at most. Then they need to stay buried undisturbed - the later floods on Mars could easily wash out all the organics, especially if they were in some soluble matrix, say salts.
Then - after spending those three billion or more years buried more than 10 meters below the surface - need to be exposed to the surface quickly within a few million years.
That's why it was so remarkable when Curiosity detected what seemed to be traces of early organics. It's not that sensitive to these things -not compared to ExoMars. Couldn't detect single molecule biosignatures.
But - this must have been quite a big deposit - and then exposed to the surface quickly - so that there were enough organics left for Curiosity to detect them.
Another thing that confuses the whole picture also - is that comets and meteorites also contain amino acids. And they also are often chiral - in pristine meteorites recovered almost immediately after they landed on the Earth - in Antarctica or in deserts - not likely to be contaminated with Earth organics - they often find a chiral excess rather like life - of one amino acid over another - and quite large excesses also.
However - distinguishable from ordinary Earth life as they tend to include amino acids not used by Earth life in its biochemistry. On Mars though detection of those amino acids would not let you tell if it was life or meteorites as of course Mars life could easily use different amino acids from Earth life.
So - even when they find biosignatures on Mars - assuming they do - is going to be a major detective puzzle to show that it is past life.
Some think that we are more likely to be able to detect present day life. The problem there is that the conditions are so harsh on Mars - that we probably are talking about just a few microbes here and there, similar to the Atacama desert, really hard to detect again. And - if we can't cultivate them either - then might be pretty hard to distinguish them.
Might spot them in microscopes. But we saw with Allan Hills 84001
These are too small for Earth life, smaller than the smallest possible modern DNA based cell. But just the right size for some earlier form of life that might have existed before Earth microbes. Perhaps they are Martian lifeforms. But the jury is out because they have inorganic explanations as well.
That could be a problem for both present day life on Mars and also ancient fossil life - if there are any fossils left for us to find.
However - does seem promising enough that we will find them eventually. Just need to hit it lucky and find a deeply buried, rapidly excavated ancient deposit still in relatively pristine state. Then might also detect complex organic compounds as well.
It also helps a lot if you can dig even a few meters below the surface.
ExoMars will be able to dig down 2 meters, which may not seem much but if you look at this graph again
It makes a huge difference. Even digging 1 meter makes a huge difference to your chance of finding billions of years old organics.
It does still have to be buried quickly - not much point digging two meters into a deposit that formed slowly over billions of years. And need to know where to dig. Not a stroll in the park :). But - if we keep looking we have a decent chance of finding good evidence of past life on Mars.
And we do have wind constantly excavating (that's what Curiosity is hoping to find, recent wind exposed ancient organics deposits) - and craters also excavated by meteorites. So - we do have a reasonable chance of finding the past life eventually.
And for present day life also - if we keep searching and use sufficiently sensitive detectors - able to detect a single organic molecule in a sample.
Oh, and there is another possible place to look for life. Deep underground, in the hydrosphere. Mars unlike Earth has a cryosphere on its surface, extending from the permafrost layer just a couple of cms below the surface, down for several kms. It's thought to be very dry for a long way down in the equatorial regions - but with some evidence of possible patches of trapped ice. Anyway - deep down it eventually gets hotter, just as on Earth - and eventually gets hot enough for ice to melt - and also - enough pressure there for water to be liquid. So - there might be, say, 100 meters maybe more depth of liquid water way down there - which might be an ideal habitat for life.
It's possible to drill down to it - are plans for unmanned landers that could drill all the way down through kms of rock using robotic moles - so maybe one day we'll get a chance to find out if there is life there. But - not the easiest target for an early search, obviously, for its depth - no matter how common or rare life turns out to be down there.
There may however be geothermal hot spots that bring liquid water closer to the surface trapped beneath layers much like the way oil gets trapped on the Earth. Also might be life in caves similarly maybe a cave that has access to a geological hot spot.
In short the main places to look are
- In the past - hard to find because it deteriorates so easily with cosmic radiation and may have been rare in the first place
- In the present on the surface - must be in extremely low concentrations - snowball Mars type phase (but with almost no water) like the dry Atacama deserts
- Deep underground - hard to access because of the depth
- In caves - again not so easy to get into a cave from the surface - but there are ideas for robots that can do that also - "cave bots" as well as caves that use cables to descend into a cave.
I think we will find it eventually. But could be a long search. Shouldn't give up for instance if ExoMars fails to find it - though I think it does have a chance of finding past life on Mars.
Even if there was macroscopic Mars life, e.g. lichens, or multicellular life forms - it might take a while to find it - after all - hard enough to find on Earth - we have different challenges on Mars. No continental drift. But lots of floods, meteorite impacts - and all the cosmic radiation toughest of all.
There might be macrofossils also - e.g. stromatolites. But if so - we need to know what they look like, with some examples, before we can identify them. Enthusiasts point out loads of "life like" formations in the rocks. But you also get things that look like like that are formed by inorganic processes.
For more about this see:
Where Should we Send our Rovers to Mars to Unravel Mystery of Origin of First Living Cells?
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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