The discussion centers on determining the necessary depth of a borehole on Mars to achieve specific atmospheric pressures, specifically 0.35 bar and 0.7 bar. Participants conclude that due to Mars' lower gravity (0.37g) and the exponential nature of pressure variation, a borehole would need to be approximately 100 kilometers deep to reach 0.35 bar. The conversation also highlights the complexities of pressure calculations, including temperature gradients and the density of CO2 compared to Earth's atmosphere. Ultimately, the feasibility of such a project is questioned, with suggestions leaning towards surface-based solutions instead of deep boreholes.
PREREQUISITESAstronomers, planetary scientists, engineers, and anyone interested in the challenges of Martian colonization and atmospheric manipulation.
Thanks. I didn't think Mars was so close to a vacuum. I was thinking a colony could compress the CO2 from say 3 psi and convert it to a breathable atmosphere with photosynthesis. At 4 or 5 psi, a slow decompression would be survivable if they were used to a low pressure, high oxygen core. But 30 Km is crazy, even 5 Km deep. Mars sucks. Wrong planet to dig to a safe psi. Might as well stick to the surface or barely below that.hutchphd said:Somebody check this: I think the surface pressure on Mars is about the same as at 30 km above earth. So the same 30 km on Mars (with .37g at surface) will get you .37 bar. So you need a 30km deep hole? Weird idea... I like it
The OP stated that the assumption was that pressure varies exponentially. This is only true in a homogeneous gravitational field so that is the approximation.russ_watters said:The difficulty with this question is that while above the surface you can use Newton's law of gravity assuming the planet is a point mass, below the surface you start having mass above you, and the gravitational acceleration strays from the curve and even decreases to zero as you get closer to the core.
30 km depth shouldn't produce all that much error.hutchphd said:If the 30km number is correct (it is beyond the warranty hour for my brain but I think that is correct) then the correction you point out is about 3% so not relevant. I will do the center of Earth (or mars) calculation tomorrow...
Yes but the OP was only looking to reach pressure of 0.35 atmospheres and so that takes care of the .37 g on mars. Well not quite...because of the exponential.Orodruin said:However, gravity on Earth is different from gravity on Mars so the coefficient in the exponential will be different so you cannot just take the 30 km and bore that deep. You will need to go deeper since Mars gravity is weaker.
Or just a regular pressure chamber ...hutchphd said:How about somehow using 10m of water instead?
The question is I think quite applicable for an investigation.sophiecentaur said:This sort of 'what if?' discussion is always worth while and the numbers can be interesting.
But I am an Engineer at heart and I was just wondering how much such a project would cost, compared with just using compressors in a surface structure. Energy storage wouldn't be a problem as the air in the dome itself would act as a reservoir for solar energy.
I seem to remember that the comparison of cost for overhead electricity cables, compared with burying them can be anything between 1/4 and 1/14. There will be many other factors that are very different between Mars and Earth but that was a figure that struck me as relevant to this discussion.
Also, what would be the knock-ons of living so far underground? You'd have to go to the surface for travel and agriculture, in any case. I am always a bit skeptical about Terraforming in general because we are very good at TerraDEforming where we already live. Could we really guarantee making things 'better' up there?