Water on Mars. Computer artwork looking east over water shining in a sunrise over Valles Marineris (Mariner Valley) on Mars 3.5 billion years ago. Mars is now a desert world, but erosion features seen on Mars today suggest that water once flowed there. The water was lost due to the thin Martian atmosphere and weak gravity. Candor Chasma canyon (centre left) and Melas Chasma canyon ( upper right) are both part of Valles Marineris, an enormous crack in the Martian crust hundreds of kilometres wide and thousands of kilometres long. The topography of this artwork was drawn with Terragen software, using data from the laser altimeter on the Mars Global Surveyor probe.