The surface of the planet Mars has two large white spots located in the polar regions, something similar to the polar caps of the Earth. In the North zone, when the cold season arrives the perpetual ice deposit is covered with frost. As the temperature drops, the frozen water disappears under a blanket of carbonic snow, which causes the polar cap to extend.
In the opposite hemisphere, the South, spring causes the temperature to rise above -120 degrees. This causes the sublimation of carbonic snow and the retreat of the polar cap. When the temperature rises to more than -80 degrees, the frost is also sublimated. At this time only permanent ice remains.
The perpetual ice mass of Mars is about 100 kilometers in diameter and approximately 10 meters thick. This means that the CO2 ice layer of the Mars polar caps is very thin, and under the South ice cap there could be water ice. In fact, NASA's Phoenix probe analyzed samples of Mars soil in 2008, finding that they contained water ice.
The polar caps of Mars have been observed just over 100 years. At this time the South polar cap has completely disappeared twice, but the North cap has never done so. The total ice mass of this last cap equals half of the ice that exists in Greenland.
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