How can I keep an atmosphere on Mars?

Question

Okay, so I'm an engineer who's been tasked with transforming Mars. I don't need to make it perfect for people to be able to walk around free with no life support. But I do need to make life, especially plant growth possible.

I know that by doing things like adding large quantities of methane to the, currently painfully thin, Martian atmosphere. Melting/sublimating much of the ice caps I can temporarily create an atmosphere, and once this manufactured atmosphere raises the planetary temperature by about 6 degrees centigrade, frozen carbon dioxide released by the planet's surface will create a generally self-sustaining/warming atmosphere.

The problem is, my best calculations only have this chain effect lasting for about a 100 years or so before my atmosphere starts to degrade and disappear again. If Mars is going to become humanity's second home, this atmosphere needs to last thousand if not millions of years. I don't want to have to "juice" the atmosphere every century or so.

I help keeping my atmosphere for thousands of years, warm, as cost effective as possible, and preferably with science/technology currently known, or likely to be developed/discovered within the 21st century.

I've tried these questions: Using temperature to contain an atmosphere? Maintain atmosphere on moon using global warming What can we do to Mars to give it a survivable atmosphere? But they're not enough. Please help!

Answer 1

I have great news, it won't be a problem for a long time.

See article on terra-forming, where a table is presented for how long atmosphere can be kept by the Moon, Mars (and other planets and moons).

The lightest important gas to maintain has a half-life of 64.5 million years, i.e., you will lose 50% of the water-vapor in the atmosphere over that span. Other important gases stick around even longer, N2 408 million years and heavier gases like O2 and CO2 even longer. Top off with some replacement gases every 10 million years and you will be good to go until the sun turns Mars uninhabitable.

Almost forgot, your methane greenhouse gas kick-starter half-life is 40 million years, so that won't be a problem either.

When you hear people says Mars is too small to retain an atmosphere, there is an understanding that it can't retain an atmosphere for billions of year - a few million years is no problem.

I did not double-check his numbers, but I assume they were based on current Martian temperatures, post terraforming I would expect you want warmer temperatures, but this change does not shift the half-lives that dramatically.

Answer 2

I have bad news...

The only thing that will naturally keep an atmosphere on a planet is gravity.

If you enter the realm of Clarkean Magic, then you can play games like an electromagnetic-ish planetary shield, useful for keeping the bad guys out, but also useful for keeping the atmosphere in. Of course, when you open the gate to let ships in and out there's a palpable Whoosh! but such technomancy would work.¹

But, insofar as we can predict a realistic future, terraforming Mars will include domes and lots of subterranean habitation.

EDIT: Curiously, we've had two basically identical questions (coming at the problem from different points of view) at nearly the same moment. Go check out my answer to (Could I use a series of magnetic asteroids to create a magnetic field for mars?) and the comments to the answer.

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_{¹ Just in case someone's tempted to suggest genetically modified planets that produce copious amounts of oxygen... plants need a source of oxygen to begin with. On Earth, it's all the carbon dioxide in the atmosphere. I don't know enough about Martian soil to know if there's enough bound oxygen in the soil that it could be released by properly modified plants into the atomsphere for long-term effects. But if you think about it, your depleting a limited resource. It's not self-sustaining.}

Answer 3

I also think there's not enough gravity to hold a decent atmosphere. Unfortunately^? "stable" systems tend to hold their state pretty well. Especially really large ones. And Mars is definitely stably dead.

Fortunately, a continuous source of energy may be able to keep a sustained hands-free atmosphere if we were willing to tweak it's composition. We need only small percentages of the atmosphere to be react-able for humans. We can fill some of the other "air gaps" with an inert chemical. It would seem to need to be a gas but could even be a solid or liquid. But it needs to have many oxygen atoms in its structure. From there soil bacteria would break it down into O₂ that we could breathe much like the Nitrogen Cycle. But in order to not escape the thin atmospheric layer we would need a method for it to recombine using energization from the Sun in the upper atmosphere. Whether there was a chemical that catalyzed the reaction or whatever. It would need to be heavier than normal air and stable as well. You'd need a similar cycle for any other light gases. The biggest questions are how dense do you need to go. And if the life present is recognizable at that point with the increasing density.

There's a likelihood that developing a whole host of solutions for all the inevitable problems of terraforming something too small is not worth the effort and that you should just pick a different target.

But maybe that's the point? Maybe this is a generational test of engineers. To make Mars one step better than was possible before. If so then just getting a basic cycle of anything to live should be doable. I think you can get certain bacteria to survive on the surface of Mars, provided enough ionization sheilding. So first doable task is magnetism or metallic clouds or something.

Or you could crush Mars. Denser planets have stronger gravity. So you could have an atmosphere... downside is there's also a stronger gravitational gradient, so you'd feel heavier in your feet than your head.

Answer 4

IMHO one method to prevent atmospheric loss is to put a roof on the atmosphere. That would prevent both loss due to the solar wind in the absence of a magnetosphere and loss due to air molecules and ions with speeds higher than the Martian escape velocity.

Percival Lowell believed that Mars was gradually loosing water and drying up due to loss of atmospheric light gases. And he believed the Martians built a vast canal system to manage their remaining water resources. But apparently Lowell never thought about more long term solutions to the problem.

Lowell published three books with his theories: Mars (1895), Mars and Its Canals (1906), and Mars As the Abode of Life (1908). At that time interplanetary space was known to be a vacuum.

So 19th century fictional space ships would have to be airtight so the air wouldn't leak out and the passengers die. Some examples include:

From The Earth To the Moon (1865) Jules Verne.

Across the Zodiac (1880) Percy Gregg.

A Journey to Other Worlds (1894) J.J.Astor.

The War of the Worlds (1897) H.G. Wells.

Auf Zewi Planeten (1897) Kurd Laswitz.

Edison's Conquest of Mars (1898) Garrett P. Serviss.

So Lowell could have read about artificial airtight enclosures with breathable atmosphere inside and deadly vacuum outside, and could have extrapolated the idea to hypothetical Martians preventing loss of the Martian atmosphere with giant artificial airtight enclosures to keep the breathable air inside. Or even eventually uniting them into a single giant worldwide artificial airtight enclosure to keep the entire Martian atmosphere inside. But apparently Lowell never suggested that could a long term strategy for the Martians.

So hypothetical future Human terraformers of Mars might not release gases into the wild and unconfined Martian atmosphere and instead use imported steel from iron-nickel asteroids to build large airtight buildings in the Hellas Basin and fill them with gases derived from asteroids with high contents of light elements. They would expand the buildings upwards and sideways to eventually fill the Hellas Basin and spread outwards to eventually cover all of Mars.

Or possibly the roof(s) could be supported by the air pressure differential in the lesser gravity of Mars. If the Martian atmospheric roof is far enough above the ground and the roofs of buildings, there may be space for aircraft to travel from place to place. Presumably pilots would be instructed to never get too near to the roof and risk making a hole in it, and if necessary to deliberately crash their vehicles rather than risk making a hole in the roof.

A breathable Martian atmosphere confined by an airtight roof above it could have a much smaller total volume and mass than a wild and unconfined breathable Martian atmosphere. And the original thin and almost useless Martian atmosphere would remain above the roof.

The thin original Martian atmosphere is still thick enough to decelerate and/or burn up meteors. in fact, because of the lower surface gravity of Mars squashing down its atmosphere much less than that of Earth, Mars has air thick enough to heat up and decelerate meteors at a higher altitude that Earth does.

So an original and unmodified Martian atmosphere above the hypothetical Martian Roof would be thick enough to stop the common grains of dust and pebbles. And no atmosphere possible on a terrestrial planet, not the atmosphere of Earth, nor the atmosphere of Titan, nor even the atmosphere of Venus, would be thick enough to stop a Chicxulub or Vredefort sized object from impacting and causing an extinction event.

If the hypothetical Martian Roof is transparent it could have coatings to cut down the intensity of ultra violent ultraviolet radiation to levels comparable to those at Earth's surface, or whatever level seems desirable. Thus those coatings on the hypothetical Martian Roof could serve the function of the ozone layer in Earth's atmosphere.

Since the Martian colonists would have to live in airtight enclosed habitats for centuries or millennia while terraforming Mars, they would lose the idea that a proper planet is one that is habitable outdoors, and become used to living in places that are only habitable indoors. Thus the idea of making all Mars an indoor world would be acceptable to them if it reduced the total terraforming time by a few centuries or millennia.

Putting a roof over the entire surface of Mars would be an incredibly vast project, but terraforming Mars is itself an incredibly vast project. But both projects would require finite and calculable amounts of matter and energy and thus would be theoretically possible.

Answer 5

Adding a magnetic field would certainly HELP a lot. A great deal of atmospheric loss on Mars occurs due to the solar wind stripping away its atmosphere, needless to say this is less of a problem with a magnetic field. This magnetic field would best be made by means of large electromagnets, which will require constant maintainence and power but are easily doable for a civilisation conolising Mars.

Answer 6

M. A. Golding suggested a roof in his answer, but I am going to scale it up. A civilization capable of doing the industrial infrastructure necessary to terraform Mars is likely to have access to a lot of energy and material. The energy comes from the Sun, and is delivered to Mars by platoons of mirrors orbiting Mars and focusing sunlight on the surface. Depending on the size and focus of the mirrors, you can warm up areas to release water and trapped gases from the permafrost presumed to exist under much of the Martian soil, to literally boiling out the oxygen trapped in the red iron oxide that covers the surface.

Water, nitrogen and organic materials can be delivered from the Asteroid belt, Titan and even cometary materials captured from deep space. A very sophisticated operation would be in place to deliver the space born materials where they were needed, and control the speed of impact to prevent blasting gasses and materials back into space.

Once you have this level of industry, it would be almost trivial to "top off" the project with a planetary sized "bubble" made of diamond to hold the atmosphere and warmth inside and slow the leakage of the atmosphere into space by geological ages. Diamond is simply a form of carbon, and artificial diamonds can already be made on Earth today, so finding a source of methane or other carmon bearing materials in the asteroid belt, the atmosphere of Titan or cometary materials gives you the starting material to create films of diamond to create the bubble.