Asked by Thomas Green
The average temperature on Mars is around -60 degrees Celsius (-76 degrees Fahrenheit) and can get even colder at the poles. This gives Mars permanent polar ice caps consisting primarily of water ice.
Like on Earth, there is seasonal variation on Mars which causes annual changes of the Martian ice caps. During the Red Planet’s winter, a pole will exist in extended periods of darkness. This makes it cold enough to allow layers of carbon dioxide to freeze, building up the ice caps. During the summer this carbon dioxide ice sublimes and the polar ice cap shrinks. The existence of these poles support the theory that Mars once had a wet and warm history on its surface.
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