Some (new) data about Mars poles

Read here.

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The Martian poles resemble Antarctica, at Earth's South Pole, because both are covered with a relatively thin layer of ice on top of rock...
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The ice caps on Mars are roughly as thick as the ice cap on Antarctica - both are about a mile-and-a-half (two to three kilometers) deep.

While the ice on Earth is made of water, Mars' ice is a combination of water-ice and frozen carbon dioxide, or "dry ice."
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Take a look also at this video: http://www.space.com/php/video/player.php?video_id=310707PhoenixMars