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Water on Mars. Image 2 of 2. Computer artwork looking east towards water in Melas Chasma canyon (upper right) & Candor Chasma canyon (upper left) on Mars 3.5 billion years ago. Ice (white) lies on the surrounding land several kilometres above the canyon floor. Mars is now a desert world, as its water was lost due to the thin Martian atmosphere and weak gravity. These canyons are part of the massive Marineris Valles (Mariner Valley) crack in the Martian crust near the equator. This image is hundreds of kilometres wide. The topography was drawn with Terragen software, using data from the laser altimeter on the Mars Global Surveyor probe. For this area today, see image R350/169. (KEYSTONE/SCIENCE PHOTO LIBRARY/KEES VEENENBOS)