A decade ago, scientists believed that sand on Mars did not shift - or moved far too slowly to be detected. But photos taken by NASA's Mars Reconnaissance Orbiter have forced a major rethink of that assumption. In fact, the Orbiter has registered literally dozens of locations where sand shifts reveal a dynamic surface undergoing change.
"We used to think of the sand on Mars as relatively immobile, so these new observations are changing our whole perspective," said Nathan Bridges, planetary scientist at the Johns Hopkins University's Applied Physics Laboratory in Laurel, Md., and lead author of a paper on the finding published online in the journal Geology.
One interesting point to note: Because the air on Mars is thin, stronger gusts of wind are needed to push a grain of sand. Wind-tunnel experiments have shown that a patch of sand would take winds of about 80 mph to move on Mars compared with only 10 mph on Earth.
The image in this slide shows the shifting in a dune found in Mars' northern polar region between June 25, 2008 and May 21, 2010. The changes included landslides and sand advancing at the dune front (upper left) as well as shifts in the position of the rest of the dune boundary relative to the fixed, underlying terrain.