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Water Ice in a Martian Crater
This image, taken by ESA's Mars Express spacecraft, shows a large patch of water ice sitting on the floor of a Martian crater. The unnamed impact crater is located on Vastitas Borealis, a broad plain that covers much of Mars' far northern latitudes. This patch of ice seems to be present all year round, as the temperature and pressure don't get high enough for the ice to sublimate away into gas. There are also faint traces of ice on the inside wall of the crater.
Fraser Cain