Mars. Mars Global Surveyor (MGS) image of clouds (white) over the surface of Mars. These high, wispy clouds mainly comprise water ice. At lower left they are seen covering the peaks of the three large Tharsis Ridge volcanoes. At far left, clouds are also seen around the peak of Olympus Mons, the largest volcano in the solar system. At top centre the ice cap covering the north pole can be seen. This image was taken by the Mars Orbiter Camera (MOC) on board the MGS spacecraft in orbit around Mars.