Desktop Project Part 17: Sculpting Martian dunes

[I have a lot of astronomy pictures I've saved to my computer's desktop, so I've pledged to post one every day in an attempt to regain control of my machine. I call this my Desktop Project.]Speaking of Martian winds... Mars is a pretty interesting place. A lot of the surface is covered in dust and sand, and while the air there is very thin, it can move with terrific speed. That gives it enough momentum to push that solid material around. The small-grained dust is far easier to pick up and get blown around by that wind, and we see lots of clear (and gorgeous) evidence of that in pictures from Mars. But the bigger, heavier basaltic sand is harder to move. Until recently there was no evidence of bulk dune motion at all on Mars*! But the fantastic HiRISE camera on board the Mars Reconnaissance Orbiter has found that evidence: the motion of a Martian sand dune that took nearly two years to see: