Is there life on Mars?
So far we
have found no evidence of life of any kind on Mars and we are virtually
100% certain there is nothing currently alive on the surface. However,
the jury is still out on whether there ever was life on Mars and also
whether it still exists below the surface.
Billions
of years ago Mars had a thick atmosphere and oceans just like Earth
does today. However over time the core of the planet cooled and froze
solid, leaving the planet without a protective magnetic field. Without
its magnetic field the solar wind stripped away its atmosphere, carrying
away 85% of the planet’s water and reducing the atmospheric pressure so
low that liquid water could no longer exist on the surface. If there
was any surface life during this period it was killed by this event. If
there was ever surface life on Mars it is likely it left behind evidence
of its existence that we should be able to detect. As yet we have not
found any such evidence but we are not yet confident that it does not
exist, since there have only been a few probes and rovers on the surface
so far and they have only covered a very small area searching.
Deep
below the surface the pressure is high enough that liquid water still
exists, meaning it is possible that life still exists deep in the soil.
We have never sent a probe capable of digging more than a few
centimeters into the surface so we have had no chance to look for life
this deep down. In 2020 the ESA will launch the ExoMars rover
which
will be capable of drilling down to a depth of 2 meters(deep enough for
liquid water to exist) with the primary aim of identifying past and
present lifeforms on Mars.
Finally, while we
go to extreme lengths to decontaminate everything we land on Mars it is
possible that we have transferred viable microbes from Earth to Mars on
one of our probes or rovers, and that these microbes successfully
started to spread on the surface, meaning that we unknowingly seeded the
planet with life
The two NASA rovers Spirit and
Opportunity, along with the recent MOM (India) and MAVEN (USA) are
currently attempting to find information that can answer the questions
about the Red Planet:
"Has there been life on Mars",
"Is there currently life on Mars", and
Your question: "Could we some day live on Mars"?
Let's take a look at the climate on Mars.
Mars is a harsh, cold world. It is much colder than Earth; because it is much farther from the Sun. (Mars is 227,900,000 km from the Sun as compared to 149,500,000 km for the Earth) The small, barren planet also has a very thin atmosphere that is 95 percent carbon-dioxide. (Scientists are exploring the possibility of extracting Oxygen from the Carbon Dioxide)
Mars's atmosphere is about 100 times thinner than Earth's. Without this "thermal blanket," Mars can't retain any heat energy. On an average, the temperature on Mars is about minus 60° C. (For Earth the figure is 16°C) In winter, near the poles temperatures can get down to minus minus 125° C. A summer day on Mars may get up to 20° C near the equator, but at night the temperature can plummet to about minus 75° C. Frost forms on the rocks at night, but as dawn approaches and the air gets warmer, the frost turns to vapor, and there is 100 percent humidity until it evaporates.
Scientists have long studied the possibility of water on Mars, analyzing evidence that suggests liquid water existed on the Red Planet in the past. Recent evidence of gullies formed within the last decade raises the possibility of liquid water on or near the surface. These findings are incredibly significant, because where there’s water there may be life.
A group of scientists in Indiana are growing small plants in Mars-like soil, in a Martian Environment Simulator, to determine whether it would be possible for astronauts exploring Mars to grow greenhouse plants on the Red Planet as a food source. Starting extremely small, with micro-organisms, the scientists have successfully shown that organic Earth-life can exist in near-Mars conditions. Starting from Algae, if we can introduce some green cover on Mars, there may be natural production of Oxygen.
"Has there been life on Mars",
"Is there currently life on Mars", and
Your question: "Could we some day live on Mars"?
Let's take a look at the climate on Mars.
Mars is a harsh, cold world. It is much colder than Earth; because it is much farther from the Sun. (Mars is 227,900,000 km from the Sun as compared to 149,500,000 km for the Earth) The small, barren planet also has a very thin atmosphere that is 95 percent carbon-dioxide. (Scientists are exploring the possibility of extracting Oxygen from the Carbon Dioxide)
Mars's atmosphere is about 100 times thinner than Earth's. Without this "thermal blanket," Mars can't retain any heat energy. On an average, the temperature on Mars is about minus 60° C. (For Earth the figure is 16°C) In winter, near the poles temperatures can get down to minus minus 125° C. A summer day on Mars may get up to 20° C near the equator, but at night the temperature can plummet to about minus 75° C. Frost forms on the rocks at night, but as dawn approaches and the air gets warmer, the frost turns to vapor, and there is 100 percent humidity until it evaporates.
Scientists have long studied the possibility of water on Mars, analyzing evidence that suggests liquid water existed on the Red Planet in the past. Recent evidence of gullies formed within the last decade raises the possibility of liquid water on or near the surface. These findings are incredibly significant, because where there’s water there may be life.
A group of scientists in Indiana are growing small plants in Mars-like soil, in a Martian Environment Simulator, to determine whether it would be possible for astronauts exploring Mars to grow greenhouse plants on the Red Planet as a food source. Starting extremely small, with micro-organisms, the scientists have successfully shown that organic Earth-life can exist in near-Mars conditions. Starting from Algae, if we can introduce some green cover on Mars, there may be natural production of Oxygen.
But whether or not astronauts
should introduce foreign organisms into the Martian environment remains
highly controversial. What right do we have to pollute Mars this way?
Science and technology have put
men on the moon, so it's very possible that there will some day be life
on Mars, overcoming all the hardships mentioned above!
Last but not least, current technologies do not exist to make traveling to-and-fro Mars a routine task. Travel times to Mars pose big exploration concerns for humans. The current estimates for a trip from Earth to Mars range anywhere from 120 days up to 260 days — and that's just one way!
Starting from 1960 to date, there have been 43 probes sent to Mars - so you cannot say we're not trying!!
Last but not least, current technologies do not exist to make traveling to-and-fro Mars a routine task. Travel times to Mars pose big exploration concerns for humans. The current estimates for a trip from Earth to Mars range anywhere from 120 days up to 260 days — and that's just one way!
Starting from 1960 to date, there have been 43 probes sent to Mars - so you cannot say we're not trying!!
There might well be. This is a new development in the last six years or so, discovery of, for instance, the warm seasonal flows
These intriguing features are very rare on Mars - not the same as the better known dry gullies (created by dry ice probably).
They form only on sun facing slopes and only when the temperatures go above zero centigrade. Far too warm for dry ice. Can't be a wind phenomenon as they aren't correlated with winds or dust storms.
They are seasonal - start off short early in the year, gradually get longer as the year progresses, and then in the autumn, slowly fade away.
All the attempts at modeling them so far assume that they are liquid water.
The problem is though - that they are very narrow streaks - and also - if there is water it is likely to be a thin layer, perhaps just a mm or so, and - no more than slightly damp regolith. Very hard to detect from orbit by isotope measurements.
Still, it would be plenty of liquid for life "living on the edge" such as microbes found in places such as the McMurdo dry valleys and the high Atacama desert.
There are several other possibilities for habitats for life on Mars. That's just the one that's hardest to dismiss as we so far have no other hypothesis for them.
Indirect evidence comes from isotope measurements by Phoenix, showing that the oxygen in the CO2 molecules in the atmosphere has interacted with liquid water in the geologically recent past. So we know, pretty sure that either there is a small amount of water on Mars all the time - or it is there episodically quite often (e.g. after asteroid impacts) - or both.
We've also detected salts on Mars - and on the Earth microbes in deserts can survive in salts that have no water at all except the water they take in from the atmosphere via deliquescence - and Mars because of the huge temperature swings between day and night has 100% relative humidity at night. Phoenix may have detected this effect accidentally, when salt deposits splashed on its legs during is landing formed dark droplet shaped objects - which then fell off - and didn't form again. It's indirect evidence as it couldn't access them to analyse what they are. But that's what started the modern search for ways that life could inhabit the surface of present day Mars.
DLR in Germany also has discovered some algae, and lichens, that are able to do the same trick and take up the night time humidity in a simulated Mars environment on their own, without need for salt deposits.
The main limiting factor - at least for Earth like life on Mars is absence of nitrogen - but Curiosity has found nitrates on Mars - and on Earth microbes can live in places with very low levels of nitrates. And nitrates should be delivered by meteorites - and most of our analyses of Mars can't see even a cm below the surface.
So seems not impossible that there are enough nitrates on Mars for life.
So - nowadays you get some researchers who are quite up beat about the prospect of finding present day life on Mars. Though others still remain highly skeptical of the idea.
As for past life -then there is increasing evidence that Mars had a global ocean - reached the point now I think where almost nobody would deny it - though it might have been frozen over quite early on and only melted sporadically. And as for Earth and Venus - it would have started off with a dense Venus like atmosphere, oceans well above boiling point kept liquid by the high atmospheric pressure - which slowly cooled down.
Depending how long evolution takes - there might well have been enough time for life to evolve before it cooled down. What's more the later snowball phase on Mars could itself have triggered evolutionary jumps - at least - the development of multi-cellular life on Earth happened immediately after its last snowball phase.
Mars as it is now is basically a "snowball" planet - it isn't white because it is also very dry and has lost most of its original water - either to space or underground or both.
Still - Earth obviously had life throughout its own snowball phases. So that doesn't mean there is no life on Mars. Just that it is very hard to detect.
Similarly if we saw an exoplanet in a snowball phase like Mars or snowball Earth - it would be just about impossible to tell whether it has life on it or not unless we can send a probe to it (not likely in near future).
So upshot is - that many scientists now think it is likely Mars had life in the past - and quite a few think it's likely it still has life.
But both types of life are likely to be hard to detect. Past life because it was habitable only for a short time, we don't yet know what to look for (what would Mars micro-fossils look like?), it might have occurred only in a few places on Mars especially right at the beginning - best chance of finding unambiguous evidence probably is through organics (unless Mars had multi-cellular life) and it's not easy to preserve organics for billions of years on Mars because of radiation in the rocks and cosmic radiation for surface deposits. Still - researchers think that we do have methods of measuring biosignatures that could detect ancient life on Mars - first instruments able to do this due to launch in 2018 on ExoMars.
For present day life - then - are all the present day possible habitats inhabited? They well might not be in such harsh conditions. And the levels of microbes are so small - it is extremely hard to detect life in the coldest driest deserts on Earth and probably even harder on Mars - and the life is likely to be hidden below surfaces of rocks or a cm or so beneath the surface of the soil.
And in both cases - we haven't yet started the search. Curiosity would not be able to detect life and distinguish it from meteorite organics except in unusual circumstances - e.g. obvious macro-fossils etc. It can find organics, but cannot easily tell if it was created by life processes, and organics (even with chirality signatures) can be delivered on comets and meteorites or formed by inorganic processes on Mars. And nothing else sent to Mars since the 1970s would be able to spot life on Mars in these low concentrations even if it looked straight at it - or put a sample containing the life into its analysis chambers. Nothing, since Viking, would be able to detect life in the McMurdo dry valleys or the Atacama desert. The Viking labelled release had that capability - but it was controversial for other reasons and for some reason, was never repeated in any later rover to address the issues discovered in the original experiment.
So the search has only just begun. We might find past life on Mars right away - even Curiosity might find it - if we are very lucky. But it might as easily take several decades.
And we have almost no chance of discovering present day life until ExoMars - and that's going to the wrong place to look for present day life so only if it is ubiquitous and easy to find. So - expect it to be some time before we start a proper search for present day life, and again that's likely to take some decades unless we are very lucky.
These intriguing features are very rare on Mars - not the same as the better known dry gullies (created by dry ice probably).
They form only on sun facing slopes and only when the temperatures go above zero centigrade. Far too warm for dry ice. Can't be a wind phenomenon as they aren't correlated with winds or dust storms.
They are seasonal - start off short early in the year, gradually get longer as the year progresses, and then in the autumn, slowly fade away.
All the attempts at modeling them so far assume that they are liquid water.
The problem is though - that they are very narrow streaks - and also - if there is water it is likely to be a thin layer, perhaps just a mm or so, and - no more than slightly damp regolith. Very hard to detect from orbit by isotope measurements.
Still, it would be plenty of liquid for life "living on the edge" such as microbes found in places such as the McMurdo dry valleys and the high Atacama desert.
There are several other possibilities for habitats for life on Mars. That's just the one that's hardest to dismiss as we so far have no other hypothesis for them.
Indirect evidence comes from isotope measurements by Phoenix, showing that the oxygen in the CO2 molecules in the atmosphere has interacted with liquid water in the geologically recent past. So we know, pretty sure that either there is a small amount of water on Mars all the time - or it is there episodically quite often (e.g. after asteroid impacts) - or both.
We've also detected salts on Mars - and on the Earth microbes in deserts can survive in salts that have no water at all except the water they take in from the atmosphere via deliquescence - and Mars because of the huge temperature swings between day and night has 100% relative humidity at night. Phoenix may have detected this effect accidentally, when salt deposits splashed on its legs during is landing formed dark droplet shaped objects - which then fell off - and didn't form again. It's indirect evidence as it couldn't access them to analyse what they are. But that's what started the modern search for ways that life could inhabit the surface of present day Mars.
DLR in Germany also has discovered some algae, and lichens, that are able to do the same trick and take up the night time humidity in a simulated Mars environment on their own, without need for salt deposits.
The main limiting factor - at least for Earth like life on Mars is absence of nitrogen - but Curiosity has found nitrates on Mars - and on Earth microbes can live in places with very low levels of nitrates. And nitrates should be delivered by meteorites - and most of our analyses of Mars can't see even a cm below the surface.
So seems not impossible that there are enough nitrates on Mars for life.
So - nowadays you get some researchers who are quite up beat about the prospect of finding present day life on Mars. Though others still remain highly skeptical of the idea.
As for past life -then there is increasing evidence that Mars had a global ocean - reached the point now I think where almost nobody would deny it - though it might have been frozen over quite early on and only melted sporadically. And as for Earth and Venus - it would have started off with a dense Venus like atmosphere, oceans well above boiling point kept liquid by the high atmospheric pressure - which slowly cooled down.
Depending how long evolution takes - there might well have been enough time for life to evolve before it cooled down. What's more the later snowball phase on Mars could itself have triggered evolutionary jumps - at least - the development of multi-cellular life on Earth happened immediately after its last snowball phase.
Mars as it is now is basically a "snowball" planet - it isn't white because it is also very dry and has lost most of its original water - either to space or underground or both.
Still - Earth obviously had life throughout its own snowball phases. So that doesn't mean there is no life on Mars. Just that it is very hard to detect.
Similarly if we saw an exoplanet in a snowball phase like Mars or snowball Earth - it would be just about impossible to tell whether it has life on it or not unless we can send a probe to it (not likely in near future).
So upshot is - that many scientists now think it is likely Mars had life in the past - and quite a few think it's likely it still has life.
But both types of life are likely to be hard to detect. Past life because it was habitable only for a short time, we don't yet know what to look for (what would Mars micro-fossils look like?), it might have occurred only in a few places on Mars especially right at the beginning - best chance of finding unambiguous evidence probably is through organics (unless Mars had multi-cellular life) and it's not easy to preserve organics for billions of years on Mars because of radiation in the rocks and cosmic radiation for surface deposits. Still - researchers think that we do have methods of measuring biosignatures that could detect ancient life on Mars - first instruments able to do this due to launch in 2018 on ExoMars.
For present day life - then - are all the present day possible habitats inhabited? They well might not be in such harsh conditions. And the levels of microbes are so small - it is extremely hard to detect life in the coldest driest deserts on Earth and probably even harder on Mars - and the life is likely to be hidden below surfaces of rocks or a cm or so beneath the surface of the soil.
And in both cases - we haven't yet started the search. Curiosity would not be able to detect life and distinguish it from meteorite organics except in unusual circumstances - e.g. obvious macro-fossils etc. It can find organics, but cannot easily tell if it was created by life processes, and organics (even with chirality signatures) can be delivered on comets and meteorites or formed by inorganic processes on Mars. And nothing else sent to Mars since the 1970s would be able to spot life on Mars in these low concentrations even if it looked straight at it - or put a sample containing the life into its analysis chambers. Nothing, since Viking, would be able to detect life in the McMurdo dry valleys or the Atacama desert. The Viking labelled release had that capability - but it was controversial for other reasons and for some reason, was never repeated in any later rover to address the issues discovered in the original experiment.
So the search has only just begun. We might find past life on Mars right away - even Curiosity might find it - if we are very lucky. But it might as easily take several decades.
And we have almost no chance of discovering present day life until ExoMars - and that's going to the wrong place to look for present day life so only if it is ubiquitous and easy to find. So - expect it to be some time before we start a proper search for present day life, and again that's likely to take some decades unless we are very lucky.
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