Martian topography. Three-dimensional map of the topography of Mars. Elevation is colour-coded, from white (highest) through red, yellow and green to blue (lowest). At far left is Olympus Mons (white), the largest volcano in the solar system. To the right of this are three other volcanoes on the Tharsis Ridge. From bottom to top these are: Arsia Mons, Pavonis Mons and Ascraeus Mons. The deep valley running right from centre is Valles Marineris, which extends over 5000 kilometres. Data collected by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor spacecraft. 27 million height measurements were made by timing laser pulses sent to Mars' surface.