The surface conditions of Mars are, to put it politely, somewhat extreme. The air pressure, temperature, and chemical conditions at the surface would individually be fatal to our species. All three together means we could only live there with some pretty advanced technology.
The average air pressure at the surface of Mars is ~600 pascals (about 0.6% of Earth's average at sea level). At the lowest altitude of Mars, in parts of Hellas Panitia, the air is twice as thick at ~1200 pascals. This is about 3.4% of the air pressure found at the peak of Mount Everest. This is far lower than the level of air pressure at which point we require pressure suits to survive.
The temperature at the surface of Mars is... cold. The experience of the rovers we've had exploring near the equator there for the last several years give us some idea of what the temperatures are like. The good news is that temperatures routinely reach above freezing, except in winter. Temperatures that we'd consider quite comfortable are even likely during a summer day. The bad news is the temperature drops precipitously at night. A routine temperature swing of a hundred degrees Celsius would be expected. Going from 50 °F to -125 °F and back across the day-night cycle would be awkward to deal with. The further we go from the equator, the colder it is going to be.
The chemistry of the Martian surface is interesting. The thin atmosphere can't absorb UV the way ours (with its ozone layer) does, so much more UV reaches the surface (even though the sun is distant enough to reduce its intensity by almost half). That higher-energy light of UV is able to drive chemical reactions in the surface layer of soil. It can break water and generate highly oxidizing compounds, making the soil surface highly reactive to organic material. (This led to the confounding results from the Viking lander life detection experiments.)
Years of biology research on Earth, however, has shown life can prosper in a far wider range of conditions than we find comfortable.
Even if the surface of Mars was entirely uninhabitable, there can still be plenty of living organisms within Mars. Life on Earth extends to as far into the rock as we've examined, with active cells living kilometers down into the crust. If there was life on the once warmer and wetter Mars (and I'm pretty certain there was), then there is certainly life still there hiding in the depths.
How about life on the surface? People have been pondering this for a while. The air pressure, temperature, and even surface chemistry are all compatible with some potential forms of microbial life. (The reactive chemicals in the soil could be consumed by microbes to fuel their own growth.) Hypothetically, even some life forms from here on Earth might be able to survive in the nicer locations on Mars.
Some researchers have been exploring this, by sampling organisms from the colder parts of our planet and exposing them to atmosphere, pressure, and UV conditions similar to what is seen on Mars. Their work showed that some lichens could not only survive the conditions there, but would actually become used to the conditions and increase its metabolism. Over time, such lichens might be able to slowly grow and spread on Mars.
That slow growth could be their downfall. Mars periodically experiences planet-spanning dust storms. Their interval isn't known precisely, but the consequence for a slow-growing lichen on the surface could be dramatic. A photosynthetic lichen which got covered in dust for too long would cease to live.
The lichens could probably persevere on vertical or slightly overhanging rock surfaces at low altitudes near the equator. (Perhaps in Valles Marineris.) They might be able to get sufficient sunlight and be protected from dust accumulation. From that foot-hold, I suspect lichens could evolve to handle the conditions and spread further. There are a few strategies that might work.
1) They could go into stasis and wait for local winds to clear away the dust. This is the strategy used by encrusting lichens here on Earth. (This is also how the Opportunity rover has managed to keep going so long.) Too much dust would still kill them, but rock surfaces exposed to wind would probably get cleared fast enough.
2) They could grow a surface which was smooth enough to not hold on to any dust, so the winds could shift it away easier.
3) They could grow into small, pointed spikes with a surface smooth enough that dust couldn't adhere. This wouldn't save them from being overcome by a traveling dune, but it might let them survive heavier dust accumulation. During clear-sky years they'd have to spend much of their energy growing upwards.
4) They could sidestep the issue by frequently shedding their resilient spores into the wind. This would ensure that some would land on the surface when the storm settled down. Even if existing colonies were killed with each storm season, some new colonies could be formed. Some would have to be able to grow from a spore to a size where they could make more spores in the intervals between killing dust storms.
Any combination of strategies could turn up given sufficient time, if they were able to survive in some protected niches initially. This process could take thousands of years or more. If we wanted to terraform Mars on any sort of human-scale timeframe, we'd have to be much more involved in adapting living things to live there.
References:
The average air pressure at the surface of Mars is ~600 pascals (about 0.6% of Earth's average at sea level). At the lowest altitude of Mars, in parts of Hellas Panitia, the air is twice as thick at ~1200 pascals. This is about 3.4% of the air pressure found at the peak of Mount Everest. This is far lower than the level of air pressure at which point we require pressure suits to survive.
The temperature at the surface of Mars is... cold. The experience of the rovers we've had exploring near the equator there for the last several years give us some idea of what the temperatures are like. The good news is that temperatures routinely reach above freezing, except in winter. Temperatures that we'd consider quite comfortable are even likely during a summer day. The bad news is the temperature drops precipitously at night. A routine temperature swing of a hundred degrees Celsius would be expected. Going from 50 °F to -125 °F and back across the day-night cycle would be awkward to deal with. The further we go from the equator, the colder it is going to be.
The chemistry of the Martian surface is interesting. The thin atmosphere can't absorb UV the way ours (with its ozone layer) does, so much more UV reaches the surface (even though the sun is distant enough to reduce its intensity by almost half). That higher-energy light of UV is able to drive chemical reactions in the surface layer of soil. It can break water and generate highly oxidizing compounds, making the soil surface highly reactive to organic material. (This led to the confounding results from the Viking lander life detection experiments.)
Years of biology research on Earth, however, has shown life can prosper in a far wider range of conditions than we find comfortable.
Even if the surface of Mars was entirely uninhabitable, there can still be plenty of living organisms within Mars. Life on Earth extends to as far into the rock as we've examined, with active cells living kilometers down into the crust. If there was life on the once warmer and wetter Mars (and I'm pretty certain there was), then there is certainly life still there hiding in the depths.
 |
| Cropped from image at [link]. |
Some researchers have been exploring this, by sampling organisms from the colder parts of our planet and exposing them to atmosphere, pressure, and UV conditions similar to what is seen on Mars. Their work showed that some lichens could not only survive the conditions there, but would actually become used to the conditions and increase its metabolism. Over time, such lichens might be able to slowly grow and spread on Mars.
That slow growth could be their downfall. Mars periodically experiences planet-spanning dust storms. Their interval isn't known precisely, but the consequence for a slow-growing lichen on the surface could be dramatic. A photosynthetic lichen which got covered in dust for too long would cease to live.
 |
| Valles Marineris circled. Image edited from [link]. |
1) They could go into stasis and wait for local winds to clear away the dust. This is the strategy used by encrusting lichens here on Earth. (This is also how the Opportunity rover has managed to keep going so long.) Too much dust would still kill them, but rock surfaces exposed to wind would probably get cleared fast enough.
2) They could grow a surface which was smooth enough to not hold on to any dust, so the winds could shift it away easier.
3) They could grow into small, pointed spikes with a surface smooth enough that dust couldn't adhere. This wouldn't save them from being overcome by a traveling dune, but it might let them survive heavier dust accumulation. During clear-sky years they'd have to spend much of their energy growing upwards.
 |
| Dr. Ian Malcom: "Life, uh, finds a way." Dr. Me: "Unless it goes extinct first." |
Any combination of strategies could turn up given sufficient time, if they were able to survive in some protected niches initially. This process could take thousands of years or more. If we wanted to terraform Mars on any sort of human-scale timeframe, we'd have to be much more involved in adapting living things to live there.
References:
- Other Mars blog posts:
- the-biologist-is-in.blogspot.com/2014/05/astrobiology-2-biology-of-mars.html
- the-biologist-is-in.blogspot.com/2015/01/astrobiology-mars-isotopic-analysis.html
- Mars air pressure:
- en.wikipedia.org/wiki/Atmosphere_of_Mars
- hypertextbook.com/facts/2003/AllisonChin.shtml
- mathscinotes.com/2012/10/earth-altitude-with-equivalent-pressure-to-mars/
- Mars temperature:
- Mars sunlight:
- www.firsttheseedfoundation.org/resource/tomatosphere/background/sunlight-mars-enough-light-mars-grow-tomatoes/
- www.nasa.gov/audience/foreducators/9-12/features/F_How_Far_How_Faint.html
- tomatosphere.letstalkscience.ca/Resources/library/ArticleId/5421/is-there-enough-light-on-mars-to-grow-plants.aspx
- ccar.colorado.edu/asen5050/projects/projects_2001/benoit/solar_irradiance_on_mars.htm
- Mars soil chemistry:
- Mars life detection experiments:
- phys.org/news/2016-10-year-old-viking-life-mars.html
- news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/
- Mars dust storms:
- www.jpl.nasa.gov/news/news.php?feature=6638
- www.nasa.gov/feature/goddard/the-fact-and-fiction-of-martian-dust-storms
- Mars elevation:
- en.wikipedia.org/wiki/Vastitas_Borealis#/media/File:Mars_topography_(MOLA_dataset)_with_poles_HiRes.jpg
- en.wikipedia.org/wiki/Valles_Marineris
- en.wikipedia.org/wiki/Vastitas_Borealis
- Extreme life:
- www.astrobio.net/extreme-life/lichen-on-mars/
- www.planetary.org/blogs/guest-blogs/20120515-earth-life-survive-mars.html
- Dust removal:
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