Martian polar scarp. Coloured satellite image of a scarp (steep cliff) at the head of Chasma Boreale. Chasma Boreale is a deep canyon in Mars' north polar region. The surface of the cliff is at far right and the base is at far left. The layered deposits (vertical lines) contain frozen carbon dioxide, water ice and minerals. They could provide clues to the planet's climate history. Image obtained by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter (MRO) on 13th September 2008. The width of this image is roughly 1.6 kilometres across.