Giant crayons on Mars

A piece of Mars: There are vast plains on Mars that display criss-crossing streaks like this. These are ~5 m (~16 feet) across, give or take. Did an alien drive a dune buggy all over, leaving behind tracks? Nope. These are the distinctive trails made by the passage of dust devils, which act like huge vacuum cleaners that suck up dust from the ground. The patterns of the tracks change every year as new dust devils churn away at the surface. (HiRISE ESP_030916_1250, NASA/JPL/University of Arizona)