Martian topography. Three-dimensional map of the topography of Mars. Elevation is colour-coded, from white (highest) through red, yellow, green and blue to purple (lowest). The Hellas Planitia impact basin is at lower left (purple). Three volcanoes (white) are seen in a line on the Tharsis Ridge (red) at centre right. From bottom left to top right, these are Arsia Mons, Pavonis Mons and Ascraeus Mons. To their left is Olympus Mons (white), the largest volcano in the solar system. 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.