Residual north polar cap

Residual north polar cap

. The portion of the north polar cap that remains in summer is a towering mountain of water ice, about 1200 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 the Viking orbiters 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. But the residual ice cover in the south (Fig. 8.16) is made of frozen carbon dioxide and is about the third the size of the one in the north. (Courtesy of NASA, JPL and the U. S. Geological Survey.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University