'Static' Mars dunes seen moving

TUCSON, Feb. 3 (UPI) -- Sand dunes in a vast area of Mars, long thought to be static and frozen in time, are moving, U.S. researchers say.

Researchers at the University of Arizona have been collecting images of the dunes using the High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter, which reached Mars five years ago. The images show sand avalanches and ripple changes in the dune fields covering an area the size of Texas at the edge of the planet's northern polar cap, a university release reported Thursday.

Scientists had long believed the dunes to be fairly static since being created long ago when winds on the planet's surface were much stronger than seen today, HiRISE investigator Candice Hansen of the Planetary Science Institute, Tucson, Ariz., said.

However, before-and-after images from HiRISE over a period covering two Martian years -- four Earth years -- show "surprising" changes, researchers found. Seasonal coming and going of carbon-dioxide ice and stronger-than-expected gusts of wind are seen as agents of change.

"This gas flow destabilizes the sand on Mars' sand dunes, causing sand avalanches and creating new alcoves, gullies and sand aprons on Martian dunes," Hansen said. "The level of erosion in just one Mars year was really astonishing. In some places hundreds of cubic yards of sand have avalanched down the face of the dunes."

In total, changes were seen in about 40 percent of these far-northern dunes during the two-Mars-year period of the study, she said.