SPACE PHOTOS THIS WEEK: Massive Galaxy Cluster, More

SPACE PHOTOS THIS WEEK: Massive Galaxy Cluster, More
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August 20, 2008--Sand dunes, seen in this July 6 HiRISE image, offer tantalizing clues to Mars's past and present.

Dunes move when consistent wind drives grains over the dune's top and down the slip face. Here slip faces suggest westward (left) movement—but dark streaks of sand being blown off the dune point southwest.

The dunes may have formed in an earlier era of plentiful sand and are now being worn away by new wind patterns.
—Image by NASA/JPL/University of Arizona
 
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