mistermack wrote:All the indications are for plenty of frozen water on Mars.
Wikipedia wrote:
The two polar ice caps appear to be made largely of water.[45][46] The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters.[47] A permafrost mantle stretches from the pole to latitudes of about 60°.[45]
Large quantities of water ice are thought to be trapped underneath the thick cryosphere of Mars. Radar data from Mars Express and the Mars Reconnaissance Orbiter show large quantities of water ice both at the poles (July 2005)[17][48] and at mid-latitudes (November 2008).[18] The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.[20]
So it doesn't look likely that much of the water escaped into space.
That's not surprising, given how cold it is. When it froze right over, it would have lost any greenhouse effect of water vapour, so it would have got colder still. And no liquid water means very slow evaporation. And the dust storms would have covered the surface of frozen seas with soil, reducing evaporation to practically nil.
The atmospheric pressure on Mars is low enough that sufficient insolation will cause water to transition directly from solid to vapor phase at temperatures as low as -170C. This is why all of the water we can expect to find away from the polar ice caps is sub-surface: any water on the surface anywhere else will boil off. The water at the poles isn't there so much because it's cold as because the angle of incident light is great enough that particulates are able to block enough of the photons to prevent sublimation. I agree that we can expect to see very little evaporation on the surface of Mars, but not with your reasoning as to why this is the case. Water will not evaporate on Mars because the boiling point for water on Mars's surface is actually lower than water's melting point due to the low atmospheric pressure.
Most things I've seen about Mars include speculation about frozen seas, so I think plenty of water is expected to be found.
Yes. At the poles and beneath the surface. Any water we can access on Mars will need to be mined and then thawed, both of which processes require an expenditure of energy which is sufficient to make leaving pools of molten water just lying around seem quite silly.
As far as the practicalities go, evaporation could be curtailed by letting the surface freeze. Heat could be preserved with insulation, which is going to be vital anway, so that wouldn't be an extra cost.
And the water that was warmest would be at depth, at a pressure of 1 bar, which would act like a pressure cooker, and prevent boiling.
Temperature is a measure of the average kinetic energy of the molecules in a substance/solution. Kinetic energy is transferred by molecular collisions. The efficiency of energy transfer is determined by the collisional cross-sections of the colliding molecules and by the mean free path of the molecule's environment. Liquid water is quite good at picking up energy and moving it around, due to the high molecular interactions and low mean free paths in an aqueous solution. Holding liquid water at any temperature above 0C would necessarily increase the incidence of energetic transfer to the layers of frozen water, increasing the probability of sublimation at the surface of the layer of ice.
If we were to position our improbably sub-aquatic Martian colony in a polar location, we would reduce incidence of sublimation at the cost of having to expend tremendous amounts of energy to keep our water in its liquid phase. If we were to position our colony nearer the equator, where noon-time temperatures on the balmiest days reach a comfortable 27C, any water not covered by an insulating layer would boil off- regardless of its phase state.
Thus the sort of colony you're proposing would require not only a protective environment for our Martian sub-mariners, but also a protective environment for their water, both to keep it from freezing solid and to keep it from boiling off. Or, in other words, instead of simply building one environment for our Martian colonists, we would have to build two. This seems rather redundant to me.
You wouldn't necessarily need huge volumes of water to pressurise a living pod. Just a thin jacket would do, so long as you maintained the correct "head" to provide the pressure.
To yield a pressure of one atm, you would need a depth of 30m (or almost one American football field) of water over an area at least equivalent to the footprint of the colony. On top of that, you would need to build some sort of insulating layer to prevent sublimation of the water; and around (and beneath) it you would need to build an insulating layer to prevent heat transfer from the massive pond into the surroundings, resulting in a rather icy environment.
Alternatively, we could simply build all these requisite insulating layers, fill the structure with an Earth-congruent atmosphere instead of water, and enjoy a massive amount of bonus habitat.
