Water on Mars
Polar caps, glacier tongues, brines, and a planet-wide inventory estimate
Fresh water surely flowed on Mars long ago. Even today, there are substantial deposits of polar ice, in dirt-covered glacier tongues at mid-latitudes, and in widely distributed subsurface brine deposits. In some mid-latitude craters or shallow slopes, exposed ice sheets up to roughly 100 meters thick have been observed, under thin cover. Radar and geomorphology suggest ice deposits buried beneath thin cover — perhaps less than one meter in some spots, on Arcadia Planetia, a low-lying plain in the lowlands northwest of the Tharsis volcanic plateau.
Water is essential to human life on Mars, not just for drinking, but also to produce oxygen, liberated along with the useful material, hydrogen, when water is electrolyzed. The total volume of water on Mars, with varying degrees of access difficulty, is estimated to be enough to cover the surface of the planet more than 35 meters deep, if it could all be released.