Originally Answered: Is it really possible for a human being to live on Mars?
Those observations were leading edge in the 1920s as it is hard to disentangle the effects of the Mars and the Earth atmosphere on the light reflected from Mars. But it is possible, using doppler effect due to speed of recession or approach of Mars, and not hard now.
Then more recently, it was found that the atmospheric pressure is also very low. It's about 1% of the Earth's atmospheric pressure, which is enough to count as a laboratory vacuum. Below 10%, the Armstrong limit, it is impossible for humans to survive more than minutes, because when the pressure is this low, your saliva boils, and the moisture lining your lungs also boils. (Some pages say that your blood boils, however, your blood is protected and won't boil except of course with an open wound, because it is contained in your veins and arteries).
So, there is no way humans can live on Mars except in spacesuits and in space habitats, supported by high technology.
There are ideas to terraform Mars. However, these would take 1000 years according to the most optimistic estimates by the Mars Society - and that is a high technology solution involving giant mirrors in space around Mars and greenhouse gas factories on the planet - and is just to get to the point where you have a dense CO2 atmosphere thick enough so that humans can survive without a spacesuit and their saliva and lung linings won't boil. But it is still, after a thousand years - an atmosphere with no buffer gas, so still poisonous, and no oxygen. In their projections, it has trees by then - but no animals or birds - and the humans would need to wear an aqualung-like breathing apparatus to survive.
Then - are ideas for oxygenating the atmosphere and adding a buffer gas - but those would take probably a few more millennia after that. For instance if you get the oxygen by photosynthesis, then the usual method of photosynthesis used by plants works by taking carbon out of the atmosphere and releasing oxygen. To do that on Mars you would need to grow enough plants and bury them to cover entire surface of Mars with organics in form of peat, or wood or whatever, to a depth of many meters - which can't happen quickly. Chris McKay estimated 100,000 years for that based on how long it takes for them to accumulate on Earth, and then taking account of the lower light levels for Mars, and also the lower gravity (which means you need about three times more mass of oxygen per square meter for the same partial pressure). And that is massively speeded up compared to the time it actually took on Earth in the past, millions of years.
But as well as that there are many differences between Mars and Earth so it is not at all sure it would work. And possible it could "unterraform" again soon after. And in any case the Mars terraforming - as usually described - is for a short time geologically. With the low gravity and lack of magnetic field that over millions of years it would probably lose its atmosphere again unless somehow continually replenished - it would also lose the CO2 to its oceans as limestone etc, because it has no continental drift to return it to the atmosphere again.
Mars probably had a thick atmosphere in the past, and if so this process has already happened and is one of the main reasons Mars is different from Earth.
All this is highly optimistic as we have never done anything like this before, also there is much that could go wrong.
Which is not to say that it is impossible. Who knows if we could do it with some as yet to be invented future technology? Even more so if we get some huge boost of understanding - e.g. through use of habitats to get a far better idea of how closed systems work - or who knows - maybe some "intergalactic library" from ETs that we pick up in radio transmissions or laser transmissions or some such, telling us in detail how to do these things and advising us about the things that can go wrong and how to prevent them / fix them.
But I think, myself, not likely with present day technology and understanding, and much to go wrong.
There are other differences also. Particularly the low gravity. Nobody knows if humans can survive long term in Mars gravity. We might be able to, maybe even better than in Earth gravity. Maybe humans in Mars gravity would live longer than they do in Earth gravity.
Or we might get seriously ill, unable to have children unless the mother is spun up to full gravity through pregnancy, impossible for children to grow up to adulthood, adult lifetimes shortened to just a few years before we die.
Nobody knows the answer there yet.
Also arguably a far better way to create habitats for humans outside Earth is to use materials from the Asteroid belt, or at first, NEOs - to create a rotating habitat. That way you can customize it as you like - with full Earth gravity, paradise-like tropical living conditions, etc, just as you like.
With Mars also there's the issue that as soon as humans land on the planet, we bring all our microbes with us - hundreds of trillions in tens of thousands of species. So there is a greatly increased risk (over robotic missions) of introducing Earth life to the planet (especially in event of a hard landing, i.e. crash).
But the very reason we want to explore Mars and to learn about it, for many, is to discover if there is any other form of life in our solar system, other than Earth life. If you bring your own life to the planet first, there is a high chance that what you discover is life you brought yourself. We can avoid this by using remote methods of exploration - either from Earth- or else exploring by telepresence from orbit around Mars using robotic "avatars" on the surface, much as players explore modern computer games.
See also my:
Trouble With Terraforming Mars
Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
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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