This dramatic premier three-dimensional visualization of Mars' north pole is based on elevation measurements made by an orbiting laser. This timing data has now been translated to a detailed topographic map of Mars' north polar terrain . The map indicates that the ice cap is is about 1,200 kilometers across, a maximum of 3 kilometers thick, and cut by canyons and troughs up to 1 kilometer deep. The measurements also indicate that the cap is composed primarily of water ice with a total volume of only about four percent of planet Earth's Antarctic ice sheet . In all it represents at most a tenth of the amount of water some scientists believe once existed on ancient Mars .
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