Gullies on a Martian sand dune. Coloured satellite image of gullies on a sand dune within Russell Crater, Mars. The source of the gullies is not known. They may have been carved in the past by liquid water, or may be a result of recent landslides. The surface also has faint tracks which were created by martian dust devils that lifts off the surface dust to reveal darker sand beneath. Image obtained by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) on 16th May 2009. The width of this image is roughly 1.2 kilometres across.