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The Global Surveyor satellite currently orbiting Mars has returned an abundance of high quality images from all parts of the red planet. Many of these show evidence for flowing water at some point in the past. Others, especially near the South Pole of Mars, show layering of ice (figs.1,2). Today liquid water quickly freezes into ice or evaporates into Mars' thin atmosphere. Temporary polar frosts which advance and retreat with the seasons are mainly condensed carbon dioxide, the major ingredient of the Martian atmosphere. But there are also water-ice clouds and dust storms, which might deposit a fine layer every year in the polar regions.
[Fig.1: Global Surveyor image of the Martian South Pole at 73.0°S, 224.5°W. Inset is for fig.2 (NASA/JPL/Caltech; Malin Space Science Systems MOC2-190, 22 November 1999).]
Among the zones of highest interest for studying Mars and the production or rentention of water ice has therefore been the layered terrain at the poles, which may contain different mixtures of dust and ice. The top meter of these layered terrains could thus record the history of many thousands of years of Martian climate and geology.
NASAs Mars Polar Lander, sent to sample the layered terrains of the South Pole, was unfortunately lost on arrival in early December, 1999. Since then, studies of Global Surveyor imagery from 2000 has revealed evidence of water drainage along crater edges. This has now been productively combined with visible light imagery from the Mars Odyssey satellite in 2001, to reveal melting snow to be a probable cause of the crater gullies.
[Fig.2: Detail of layered terrain at South Pole of Mars, showing an area 1 by 3 km. (NASA/JPL/Caltech; Malin Space Science Systems MOC2-190, 22 November 1999).]
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