02-22-2020, 02:45 PM | #11 | |
Join Date: May 2005
Location: Oz
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Re: [Space] Getting Mars to 1% hydrographic coverage
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In other words, if you put a lot of water on the surface of Mars it would boil owing to the low pressure, and go on boiling until either it established an atmosphere of water vapour with enough pressure to halt the boiling, or boiled away short of that point. If you added enough other gasses to suppress the boiling then the same amount of water vapour would evaporate off as boiled off in the other case, and the water vapour component in the total atmosphere would be as massive as the atmosphere of water vapour in that other case. EXCEPT THAT the other gas you added would exert a greenhouse effect, which would warm the surface, raise the saturated vapour pressure, increase the amount of water vapour in the atmosphere, and cause more water to evaporate away from the liquid bodies. And if you are thinking about the thermal escape of water vapour to space (Jeans escape), that's controlled by temperature, molecular mass, and the escape velocity. Through it may be termed "boiling off to space" it's more like an evaporation; pressure doesn't come into it.
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02-22-2020, 03:08 PM | #12 |
Join Date: May 2005
Location: Oz
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Re: [Space] Getting Mars to 1% hydrographic coverage
It might be attractive to start making your first lake on Mars at Hellas Planitia, which is a vast impact basin seven kilometres deep. It is deeper and smaller than the northern polar basin, so it would be easier to fill with a pool of vapour, and it already retains a barometric pressure twice that at the datum elevation.
To a certain extent, Hellas Planitia might be where your water ends up whether you want it to or not.
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02-22-2020, 03:25 PM | #13 |
Join Date: Mar 2005
Location: Maitland, NSW, Australia
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Re: [Space] Getting Mars to 1% hydrographic coverage
It isn't possible to terraform Mars without a thicker atmosphere and the atmosphere isn't possible without restoring the planet's magnetic field. Without a magnetic field, any atmosphere you try to build will be stripped away by the solar wind.
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02-22-2020, 04:06 PM | #14 |
Join Date: May 2005
Location: Oz
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Re: [Space] Getting Mars to 1% hydrographic coverage
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.
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02-22-2020, 04:24 PM | #15 |
Join Date: Mar 2008
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Re: [Space] Getting Mars to 1% hydrographic coverage
Can't find tha article I read years ago but it had the Moon retaining a breathable atmosphere for at least 10s of thousands of years if you created one on it. So at least that long I'd say, maybe 100s of thousands.
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02-22-2020, 05:31 PM | #16 | ||
Join Date: May 2010
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Re: [Space] Getting Mars to 1% hydrographic coverage
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02-22-2020, 07:00 PM | #17 | ||
Join Date: May 2005
Location: Oz
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Re: [Space] Getting Mars to 1% hydrographic coverage
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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.
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Decay is inherent in all composite things. Nod head. Get treat. Last edited by Agemegos; 02-22-2020 at 07:01 PM. Reason: footnote |
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02-22-2020, 07:16 PM | #18 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Space] Getting Mars to 1% hydrographic coverage
To be fair, on the scale of terraforming, making a superconducting loop magnet capable of shielding a planet isn't all that big.
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02-22-2020, 07:22 PM | #19 |
Join Date: Aug 2007
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Re: [Space] Getting Mars to 1% hydrographic coverage
You could dig a tunnel from pole to pole through Mars' dead core and set up a rather large bar magnet as an alternative.
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02-22-2020, 08:16 PM | #20 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: [Space] Getting Mars to 1% hydrographic coverage
Dunno how hard that would be, but in general the handy thing is that the energy content of a magnetic field is proportional to volume times intensity^2, and the intensity required is inversely proportional to the radius of the screened volume, so the energy requirement is linear in radius. It's generally going to beat mass shielding for more than a few hundred meters or maybe a kilometer.
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