Martian polar ice caps

Water ice deposits on the poles of Mars

The planet Mars has two permanent polar ice caps of water ice and some dry ice (frozen carbon dioxide, CO2). Above kilometer-thick layers of water ice permafrost, slabs of dry ice are deposited during a pole's winter, lying in continuous darkness, causing 25–30% of the atmosphere being deposited annually at either of the poles. When the poles are again exposed to sunlight, the frozen CO2 sublimes.

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