This drawing shows a cross-section of the Martian frozen ground.
Click on image for full size
The Martian Cryosphere
The Martian geography is one of high altitudes at high southern latitudes and low altitudes at low latitudes.
The ground is less frozen at low latitudes because it is warmer and water can evaporate. Thus, at low latitudes (near the equator) the ground is possibly devoid of water to a depth of 200 m, while at high latitudes (corresponding to high altitudes) the ground is devoid of water to a depth of only 1 m. Another way of saying the same thing is that the frozen ground is only 2.5 km deep at the Martian equator while it is 6 km deep at the south pole.
The figure shows a crossection of the crust, and the unusual altitude variation of the Martian surface. The figure illustrates the depth of frozen ground at various latitudes, called the cryosphere, as well as the depth to which the aquifer, or layer of liquid water, may exist across the planet. To have liquid water running on the surface of Mars, the aquifer, or liquid region, must be exposed to the surface. This may have happened at various times in the history of Mars as the climate changed.
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