dark streaks of sediment on the downwind side of the dunes on the surface of Mars. They were created by escaping gas from the evaporating carbon dioxide ice below. The bottom of the ice melts into vapour and moves toward holes in the ice, carrying dark sediment along with it that is then deposited when the gas escapes. This image was taken by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter in April 2008.