[Space] Getting Mars to 1% hydrographic coverage

Michael Thayne · 02-21-2020, 01:45 PM

Terraforming Mars is unlikely to be easy. This got me thinking: what's the minimal amount of Mars terraforming that would be interesting in GURPS terms? Looking at the habitability rules in GURPS Space, I notice that any hydrographic coverage, even 1%, is good for +1 to habitability. So what would it take to get Mars there?

My understanding of the physics is that in order to have liquid water of the long haul, you first need to add lots of water vapor so that the water vapor and liquid water can be in equilibrium. Average surface temperatures of a newly-terraformed mars are likely to be just above freezing, so we can probably use the vapor pressure of water at 0 C for these estimates, which happens to be just over 0.006 atm, coincidentally roughly equal to Mars' current atmospheric pressure. So we're talking about getting Mars' atmospheric pressure to at least 0.012 atm, which is technically no longer "trace" atmosphere according to GURPS but instead "very thin", not that that will do much for Mars' habitability by itself.

At first I thought this would also mean doubling the mass of Mars' atmosphere, but given that Mars' atmosphere is mostly CO2 and IIUC gas pressure is a function of number of molecules rather than mass, we might only be talking about a 40% increase in the mass of Mars' atmosphere. Since Mars' atmosphere is about 25 trillion tons, that means we need about 10 trillion tons of water. My big question is: how much of that could you get by melting Mars' polar ice caps with big solar mirrors? That, I think would represent less than 1% of the ice found in Mars' polar caps, though I really don't know how much of those you're going to melt even with solar mirrors that get the average surface temperature above freezing.

So, people who have more expertise on this sort of thing than I do, what say ye?

02-21-2020, 01:45 PM	#1
Michael Thayne Join Date: May 2010	[Space] Getting Mars to 1% hydrographic coverage Terraforming Mars is unlikely to be easy. This got me thinking: what's the minimal amount of Mars terraforming that would be interesting in *GURPS* terms? Looking at the habitability rules in *GURPS Space, I notice that any hydrographic coverage, even 1%, is good for +1 to habitability. So what would it take to get Mars there? My understanding of the physics is that in order to have liquid water of the long haul, you first need to add lots of water vapor so that the water vapor and liquid water can be in equilibrium. Average surface temperatures of a newly-terraformed mars are likely to be just above freezing, so we can probably use the vapor pressure of water at 0 C for these estimates, which happens to be just over 0.006 atm, coincidentally roughly equal to Mars' current atmospheric pressure. So we're talking about getting Mars' atmospheric pressure to at least 0.012 atm, which is technically no longer "trace" atmosphere according to GURPS* but instead "very thin", not that that will do much for Mars' habitability by itself. At first I thought this would also mean doubling the mass of Mars' atmosphere, but given that Mars' atmosphere is mostly CO2 and IIUC gas pressure is a function of number of molecules rather than mass, we might only be talking about a 40% increase in the mass of Mars' atmosphere. Since Mars' atmosphere is about 25 trillion tons, that means we need about 10 trillion tons of water. My big question is: how much of that could you get by melting Mars' polar ice caps with big solar mirrors? That, I think would represent less than 1% of the ice found in Mars' polar caps, though I really don't know how much of those you're going to melt even with solar mirrors that get the average surface temperature above freezing. So, people who have more expertise on this sort of thing than I do, what say ye?