Atmospheric density development during terraforming.

Small question from a non-sciency person. Say we found a cheap, efficient way to terraform Mars. Leaving aside all the issues that raises would the atmosphere as it grows denser "puddle" in the low points first?

And if the above is correct what are some of the most obvious candidates for that puddling?

TIA

 

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No not really. However the density of the atmosphere would be higher in the lower elevation areas, just like on earth.

 

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"You can have cheap and good but it isn't fast.
You can have cheap and fast but it isn't good.
You can have good and fast but it isn't cheap."

 

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Yes, just as on Earth.

If you dug a hole 12 miles deep, atmospheric pressure would be approximately 4psi. You could live in that with nothing but an oxygen mask (atmosphere would still be pure CO2.) You might be able to get some plants to grow.

At those depths it would be fairly hot - ground temps would be around 90C. Air temps would not be as high, but it might well be unlivable. (Air temperature would be a combination of conduction from the ground and adiabatic heating of air.)

So the challenge would be to find a depth that gives you a pressure above about 2psi (minimum survivable pressure) while not getting too hot. The deepest trench on Earth is 7 miles; deepest on Mars is 5 miles. At that deepest point pressure is .2psi right now. So you'd have a lot of digging to do. (Alternatively you'd have to add a lot of air.)

 

Nope, I neglected the difference in gravity in the above, resulting in a higher approximate pressure.

Using a more accurate approximation I now get ~2.5 PSI and ~42 degrees F average in a hole 22 miles deep due to atmospheric phenomena. Again, the planet will be considerably warmer at those depths and that has to be accounted for as well. If the surface temperature works out, you could create an "oasis" that could retain both liquid water and a plant-friendly atmosphere.

 

Valles Marineris, which is 2490 miles long & as deep as 7 km (4 mi) and as wide as 200 km (125 mi), so, what, maybe in the neighborhood of 1M cubic miles of puddle? I think there was a SciFi story which had incorporated the idea you have.