Permafrost

Buried water that freezes and does not melt in summer is called permafrost. This is common in polar regions on Earth, but on Mars it is planet wide.

It is estimated that permafrost reaches down to about 1 km. Below that depth, it is warm enough (and under enough pressure) to form liquid water. Many bacteria live at such depths on Earth, and if Mars ever had life, it is likely that it still survives in these deep aquifers.

In areas of geothermal activity, it is likely that the permafrost is much shallower.

Ice in the soil can exist buried only millimetres deep (near the poles) to several meters deep (in warm areas near the equator). However, over most of Mars ice is stable from 10 to 100 cm below the surface. Above 60 degrees latitude, ice is found everywhere in the soil.

Permafrost makes a fine foundation for structures, so long as it is not heated to melting temperature.

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