In December, the rover Curiosity reached some sand dunes on Mars, giving us the first views of these dunes taken from the ground instead of from above. It’s impressive how the dune seems to shoot straight up from the rocks here!
In fact this slope—the steep downwind slope of one of “Bagnold Dunes” along the northwestern flank of Mount Sharp—is just about 27°. But mountaineers will confirm that slopes always looks steeper than they are.
The wind makes this dune move about one meter per year.
For more, see:
• NASA, NASA Mars rover Curiosity reaches sand dunes, 10 December 2015.
• Jet Propulsion Laboratory, Mastcam telephoto of a Martian dune’s downwind face, 4 January 2016.
• Jet Propulsion Laboratory, Slip face on downwind side of ‘Namib’ sand dune on Mars, 6 January 2016.