Current knowledge suggests there is plentiful water ice at the Martian poles. The same knowledge says it gets cold enough at the poles for carbon dioxide to freeze out of the air. If creating a habitat towards the equator of Mars (to have slightly warmer temperatures) we will need to get these gases somehow closer to the habitat.

Oxygen and hydrogen combine to form water. These are probably the most critical elements required in large quantities to sustain human life. Oxygen to breathe and hydrogen to combine with oxygen to make drinking water.

This answer suggests there is plentiful oxygen trapped in the soil as iron oxide & hydroxides which contain both oxygen and hydrogen.

How much soil would need to be processed to extract a gallon of water?

How much soil would need to be processed to fill a 10' x 10' X 10' room with the same amount of oxygen in the same room on Earth?

  • $\begingroup$ Oxygen can also be obtained from atmospheric $CO_2$ with enough energy. Hydrogen is the limiting resource. $\endgroup$ – Steve Linton Nov 20 '18 at 23:48

Assuming you could extract all the water from the soil, which apparently has roughly 2% of it by weight (by the way, that's really dry and even the driest of desert sands contain more), then you'd need at least 189.27 kg (417.27 lb) of Martian soil to produce one gallon (≈ 3.79 liters) of water. This would be extremely difficult to do though and would require a lot of power, probably to first grind it as fine as you can, then superheat, separate vapor through microfiltration and condense.

If we assumed this same water would later be used to extract oxygen through electrolysis (88.8% of its molecular mass is oxygen), and you'd want about the same oxygen contents as in average sea-level Earth atmosphere (oxygen at 23,14% of molecular mass of air at its total weight of 1.2 kg/m3), you'd require ≈ 6.98 liters (1.84 US gal) of water to fill a 10x10x10' (28.3168 m3) room with it. Assuming I didn't misplace some decimal point in my unit conversions, but it seems about right.

  • 2
    $\begingroup$ Even dry dog food is generally said to contain about 10% water. And dry dog food is pretty... dry. $\endgroup$ – user Nov 29 '16 at 13:48

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