Sand dunes in motion on Mars
"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.
In this image: sand in Mars' Becquerel Crater moved about two yards between November 24, 2006 and September 5, 2010. The white line tracks the displacement between two ripples.