[Space] Getting Mars to 1% hydrographic coverage

[Michael Thayne]

Originally Posted by Agemegos

What? The boiling point is a temperature.

Blah, I meant to say "pressure".

I don't think that is correct.

A liquid boils at the temperature where its vapour pressure is sufficient to open a bubble against the ambient pressure. So high pressure will suppress boiling, i.e. raise the boiling point. Whenever you see a liquid boiling it must be the case that its saturated vapour pressure is higher than total ambient pressure, and that means that its saturated vapour pressure must be higher than the partial pressure of its vapour above it. And that is the definition of the air above it not being saturated with vapour. A saturated vapour always exerts enough pressure to prevent boiling at the ambient temperature¹; an unsaturated vapour admits evaporation even if the liquid is not boiling.

So it doesn't matter whether the liquid is boiling. What matters is whether the vapour above it is saturated. If not, your lake or sea will evaporate and blow away even without boiling.

_______
¹That's how pressure-cookers work.

Ah, okay, you've got me convinced.

[Michael Thayne]

Anyway, back to my original question: so we're looking at needing >25 trillion tons of water. Given gargantuan solar mirrors of the sort needed to heat Mars to Earth-like temperatures over the long run (like possibly a few centuries), how long is it going to take to melt a few tens of trillions of tons of Martian polar ice?

[awesomenessofme1]

Originally Posted by Michael Thayne

Anyway, back to my original question: so we're looking at needing >25 trillion tons of water. Given gargantuan solar mirrors of the sort needed to heat Mars to Earth-like temperatures over the long run (like possibly a few centuries), how long is it going to take to melt a few tens of trillions of tons of Martian polar ice?

I did some quick math on this, and the answer, for all intents and purposes, is "a ludicrous amount." Using metric for convenience:
1 metric ton = 1 Mg = 1x10^6 g
25 trillion = 2.5x10^13
The enthalpy of fusion of water is 3.3355x10^2 J/g
Multiply it all together and you end up with 8.4x10^21 J, or 8.4 ZJ.
For reference, a spinal battery on a SM+15 capital ship does a mere 3 TJ, 3 billion times smaller.

EDIT: I did a bit of looking things up, and I found an estimate that about 4.2e15 W of solar energy hits Mars. That means that if you could somehow take 100% of that energy and devote it to melting ice, you could actually do it rather quickly, in around 24 days. Practically speaking, it would take much, much longer.

[AlexanderHowl]

You would need around 5 quadrillion metric tons of water to get to 1% hydrographic coverage for Mars (based on the relative area). There is not really enough ice on Mars (the ice on the polar caps have around half that amount), so you would need to get the rest from the Main Belt. One thing of concern is the MMWR, which is 35 for Mars (at 225 K), meaning that it cannot hold water vapor.

[DanHoward]

Originally Posted by Agemegos

How quickly, though? If we had the absurd shipping capacity to supply Mars with an atmosphere to start with we might be able to keep it topped up.

Right now the atmosphere is losing 100g per second but the rate was apparently faster when the atmosphere was thicker.

[dataweaver]

On top of all of this, there's the question of whether there might be a better use of your time and effort. Like, say, constructing space habitats.

[Agemegos]

Originally Posted by dataweaver

On top of all of this, there's the question of whether there might be a better use of your time and effort. Like, say, constructing space habitats.

Burn the heretic!

People like you say "when we can reach the stars we won't need planets".

[AlexanderHowl]

Now, if Mars was more Earth-like, I would agree that it should be terraformed, but there is a legitimate question of whether that would be a good use of resources. Since the thread is about terraforming Mars though, we will assume that it is a good idea. Anything that we can produce on Mars, such as oxygen for water, carbon dioxide, etc., will greatly reduce the mass needing transport though.

Now, there is a chance that Mars has massive amounts of volatiles trapped underground (we actually know very little about the geology of Mars). If so, there is likely microbial life still clinging on due to geothermal heat (contrary to popular belief, Mars does possess a partially molten core, the reason why it lacks a magnetic field is because the molten core is only a relatively thin boundary layer, unlike Earth's core). Introducing warmth to release volatiles will likely cause the microbial life to return to the surface.

At that point, it really matters if the ancient microbial life of Earth, Mars (nearly frozen to extinction), and Venus (cooked to ash) shared a common origin. If they did, then Martian microbial life could potentially infect Earth life and, without any immunity, Mars could be a death trap. If they did not, Martian microbial life may be scientifically interesting, but likely only a minor nuisance.

[Michael Thayne]

Originally Posted by awesomenessofme1

I did some quick math on this, and the answer, for all intents and purposes, is "a ludicrous amount." Using metric for convenience:
1 metric ton = 1 Mg = 1x10^6 g
25 trillion = 2.5x10^13
The enthalpy of fusion of water is 3.3355x10^2 J/g
Multiply it all together and you end up with 8.4x10^21 J, or 8.4 ZJ.
For reference, a spinal battery on a SM+15 capital ship does a mere 3 TJ, 3 billion times smaller.

EDIT: I did a bit of looking things up, and I found an estimate that about 4.2e15 W of solar energy hits Mars. That means that if you could somehow take 100% of that energy and devote it to melting ice, you could actually do it rather quickly, in around 24 days. Practically speaking, it would take much, much longer.

I did the same math and got the same results. A big question, I think, is how cheaply you can manufacture materials for big orbital mirrors to redirect sunlight to Mars' poles. GURPS Mars claims that in terms of the amount of material needed, a solar mirror based project might be comparable to building a large dam—a big project, but doable. But arguably even with advanced technology we should expect big orbital terraforming mirrors to be much more expensive in terms of cost per weight than a big dam.

[Prince Charon]

Originally Posted by AlexanderHowl

That would not be a good idea, for a couple of reasons. First, the relative orbital velocity of Venus around the Sun is around 10 km/s, meaning that the velocity of the atmosphere would exceed the escape velocity of Mars.

Which only matters if your wormhole maintains the exact velocity relative to the source location upon exiting, including direction, rather than being relative to the position of the wormhole moth that it's exiting from. That's not the case in every setting.