A Piece of Mars: These rocks look like hooded figures from some dark fantasy story. European standing stones should be jealous, they don’t typically get a shroud of dark sand to add to their mystery and etch them into beguiling shapes (but then perhaps they don’t need it). Here, sand moving from the upper right to lower left slowly carves out these lovely shapes. (PSP_007535_1755, NASA/JPL/Univ. of Arizona)