"NASA Probe Discovers Rolling Rocks, Gullies, Shifting Sands on Mars

Space - Discover magazine science:

"Sightings of shifting sand dunes, rolling boulders, and a dwindling polar ice cap in the past year demonstrate that the Red Planet is a far more dynamic world than scientists suspected.

Recently released images from the Mars Global Surveyor show before (left) and after views of the same crater, taken 13 months apart. During that time, falling boulders carved at least a dozen new tracks into the fine-grained material that lines the crater's wall.

NASA's orbiting Mars Global Surveyor revealed fresh gullies as long as three football fields on a dune west of the Hellas Basin. The same slope was smooth and unblemished in 2002. Scientists suspect that carbon dioxide trapped beneath the surface during winter vaporized when temperatures rose, releasing gas and causing sand to pour down the dune's face. The probe also snapped photos of boulders that had tumbled down a five-mile-wide crater, gouging shallow troughs not seen a year before. Possible causes include wind and seismic activity, although Mars's atmosphere is one-hundredth as dense as Earth's, and researchers have not yet found reliable evidence of Marsquakes. Meanwhile, carbon dioxide ice at the south pole has dwindled for three consecutive summers, suggesting long-term climate change is under way."