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Mars South Polar Cap

Image of Mars South Polar Cap
A LITTLE TO THE LEFT: Like Earth, Mars has frozen polar caps, but unlike Earth, they are made from carbon dioxide ice as well as water ice. During Summer in the Martian southern hemisphere, much of the CO2 ice sublimates (turns directly from ice to vapor), leaving behind the “residual polar cap.” The Winter polar cap is symmetrical about the south pole, but the residual cap is offset a few degrees…why? Climate data from the European spacecraft Mars Express revealed that the south polar cap is actually built up every year by two different weather systems—one that produces CO2 snow on the western side of the pole, and another in which only ground frost occurs on the eastern side. Frost sublimates more readily, and when it disappears, the snow-built cap to the west of the pole is all that’s left. Image Credit: NASA/JPL-Caltech/University of Arizona
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