Martian surface. Artwork of the Terra Sirenum area in Mars' southern hemisphere, which is dominated by old, heavily cratered highlands. The large crater with a central peak at upper right near the horizon is Liu Hsin, with a diameter of 130 kilometres. Just beyond Liu Hsin is the southern rim of a much larger crater Copernicus, with a diameter of 290 kilometres. At left high altitude cirrus clouds of water ice crystals have formed in the carbon dioxide atmosphere.