The terraforming of Mars, assuming that the hurdle of establishing a magnetic field has already been jumped, now meets another problem: water. The planet has a pair of ice caps, but between them they haven’t enough water to fill all of the Great Lakes, let alone cover 50% of the surface in water as the planet may once have been covered. So, other sources of water are necessary. Cometary bombardment appeals, but I can’t find any comets that orbit near mars. Phobos may contain large amounts of ice, so it could be used, but are there any other named bodies near mars that contain large amounts of ice?
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2$\begingroup$ Just look the way that K.S. Robinson did it in the Green Mars trilogy: Just claim there's humongous amounts of water ice underground (which with the current data, we cannot exclude). $\endgroup$– AtmosphericPrisonEscapeCommented Dec 9, 2022 at 18:39
6 Answers
No easy way to do it
Mars in unlikely to contain vast oceans of water in any discreet way. However, there's plenty of ice in the solar system. If you're serious about this terraformation thing, you'll need to put in the work to make it happen. You said there are no nearby comets. Well, orbits can be changed.
You'll find some sources of ice in the asteroid belt and much more in the outer solar system. Jupiter, Saturn, etc. Automated rockets/drones will need to be built and deployed en masse to millions of targets throughout Sol, adjusting the objects' paths to intersect Mars in the coming decades.
And if you're looking to fast-track things, and if you have torch drives or a vast beam power network, those rockets may need to push their target objects on non-Keplerian/brachistochronic trajectories.
Are you looking for a serious scientific discussion of how to terraform Mars? Or something that would work for a science fiction story?
If (b), the answer is simple: Make something up. Just blithely say that explorers found large quantities of ice or liquid water beneath the surface. Say that they found an asteroid made of ice and attached rockets to it to redirect its orbit to collide with Mars. Or say that scientists have invented some chemical process that quickly and efficiently turns some chemical in the Martian soil or atmosphere into water.
So, this is total spitballing on my part but was inspired by the OP having already solved the problem of mars having no magnetic field, relies heavily on that assumption and how it might work.
Mars has an abundance of carbon dioxide and carbon monoxide. Not much Hydrogen as it gets blow away from the thin atmosphere by the solar wind. Ironically the solar wind contains an abundance of hydrogen.
Step One: Shield Mars from the harmful radiation and solar wind, in the same process harvest hydrogen from the solar wind.
Step Two: split CO2 into C and O2 in the martian atmosphere. Sequester the carbon from recombining with the O2 buy combining it into carbon-silicate
Step Three: After oxidation of the atmosphere is complete begin catalyzation of collected hydrogen and oxygen into water.
Obviously this will require enormous amounts of energy over a quite a long time. I have only a vague idea of the density of hydrogen contained in the solar wind, nor its rate of flow and how big of a collector needed. So how long this would take IDK. Your fault for not asking for hard science :D
Additional thoughts: Precisely yeeting the 4 largest asteroids (roughly 60% the total mass of the entire belot in just those 4 Ceres; Vesta, Pallas, and Hygiea) into Mars to add whatever water and their mass to Mars may speed the process. OR... perhaps Give mars a decent moon MIGHT have beneficial results as does Earth's Moon.
Mass drivers installed on Europa aimed at Mars could be an interesting delivery system.
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$\begingroup$ What is carbon silicate? $\endgroup$– user86462Commented Dec 10, 2022 at 10:30
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$\begingroup$ @SeanOConnor en.m.wikipedia.org/wiki/Silicon_carbonate $\endgroup$ Commented Dec 10, 2022 at 20:48
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$\begingroup$ space.stackexchange.com/a/45984/15771 has some numbers on the density issues. You would need an utterly gigantic collector to make this work. You would also need to brake the hydrogen by a couple hundred km/s, and there's nowhere near enough CO2 to make all the water you need for terraforming. Just go grab some comets. $\endgroup$ Commented Dec 11, 2022 at 14:43
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$\begingroup$ @ChristopherJamesHuff the discussion seems to bolster this idea. Agree that the apparatus to collect that much H, would be ludicrously large perhaps the HxW of a planetary magnetic field. Which is what I proposed. In any case a magnetic field or something solving the problem being nessisary. Why not have it serve dual purpose. And in the least case it could help maintain an established atmosphere. $\endgroup$ Commented Dec 11, 2022 at 15:57
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$\begingroup$ ...it really doesn't. Mars has 0.28 times Earth's surface area. Scaling the water requirements with surface area, Mars needs about 4e16 t of hydrogen to match Earth. If you captured all of the sun's solar wind with 100% efficiency, it'd take about a thousand years to collect enough hydrogen. If you only caught what came within half an AU or so of Mars (a magnetic bubble that would reach Earth when the two planets pass each other), that goes up to about 40 thousand years. And the secondary purpose isn't really needed, once you've constructed an atmosphere it'll remain for millions of years. $\endgroup$ Commented Dec 11, 2022 at 18:33
Make your own water.
Mars has plenty of mass. People call it "Mars". If you want water all you need to do it take that Mars stuff apart and put it back together as water.
Iron, for example. Lots of that on Mars. An atom of iron has 30 protons. Bust them up. Now you have 30 hydrogen atoms! You can hook a couple of them to the oxygen that used to be with the iron and get a molecule of water. Now you have 28. You can make 2 oxygen atoms (8 protons each) and 4 more hydrogens and viola! 2 more molecules of water. You have some protons and neutrons left over; save those for later.
"But but but but" you protest wetly. "Busting up the iron atom takes a lot of energy!" Short on energy, are you? Perhaps Mars is too ambitious. Maybe you can work on terraforming Kansas.
Instead of a few big rocks how about lots of little ones?
I'm imagining some kind of autonomous drone swarm. Details are up to you but a drone might look like this:
A small nuclear reactor for long-lasting power. Some kind of robotic arms/tools/etc. to interact with the rocks they encounter. A rocket engine. And some way to convert ice into Hydrolox for fuel.
A drone attaches to some rock. Extracts ice to replenish its fuel. Adjusts the rock's orbit so that it intersects with Mars in the next, say, 10 years. Then takes off for the next rock that needs adjusting.
If you've got a swarm of these moving around the solar system then you could accomplish a lot over the course of a decade.
Crash a moon into it
If your civilisation has advanced to the point where they are terraforming planets then you can do some pretty big things.
If you don't mind destroying everything on the surface in the process, there are several moons and other bodies in the solar system with enough water to cover the planet in one go.
Here's a helpful chart of the largest bodies of water in the solar system (based on current estimates). Mars has a volume of ~163 ZL so the top 3 would be closer to crashing Mars into another Mars. But hey if we're gonna be terraforming anyway maybe you want to make it a bit bigger.
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$\begingroup$ you would also render he surface uninhabitable for millions of years just due to heating back to molten if you drop it all one once, plus al ot of it gets blown back out into space, better to do many smaller drops. $\endgroup$– JohnCommented Dec 11, 2022 at 4:26