Permanent, residual north polar cap of Mars

Permanent, residual north polar cap of Mars

Fig. 8.11 . The portion of the north polar cap that remains in summer is a towering mountain of water ice, about 1.2 thousand kilometers across. The summit, which nearly corresponds with the planetís spin axis, stands about 3 kilometers above the flat surrounding plains. The north residual cap is surrounded by a nearly circular band of dark sand dunes formed and shaped by wind. This image, which was acquired by a Viking orbiter during the northern summer of 1994, strongly resembles that taken by the Mars Global Surveyor in the northern summer of 1999. Both the north and south residual caps contain deep valleys that curl outward in a swirled pattern that has been cut and eroded into the icy deposits, like a giant pinwheel. (Courtesy of NASA/JPL/USGS.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University