Barely a dune

A piece of Mars: What makes a dune different from a random pile of sand? Usually the requirement is that it has a “slipface”, a steep avalanching slope. The central dune in the image here has a small one, making it a type of dune called a barchan. The other dunes are called “dome dunes”, because they don’t have proper slip faces. It is arguable that they aren’t really proper dunes at all. (HiRISE ESP_027378_2540)