Sands of Time by National Geographic

Sands of Time

Images courtesy University of Arizona/Caltech/NASA

The sands of Mars are surprisingly shifty, according to a new analysis of pictures taken by NASA's Mars Reconnaissance Orbiter over two years.
Dune fields covering an area the size of Texas form a band around the edge of Mars's north polar ice cap. Scientists had thought these dunes were frozen in time, shaped long ago by much more powerful winds than the area experiences today.
But a series of three images of the same dune shows avalanches and noticeable changes in the ripple patterns between 2008 and 2010. The scientists think that, instead of by winds, the sand is being reshaped by carbon dioxide gas released as the seasonal ice cap vaporizes and reforms.

Published February 10, 2011