Distribution of subsurface water on Mars from Odyssey
The colors in this map portray the distribution of water in the subsurface of Mars. To produce this map, Mars Odyssey's neutron spectrometer detected the amount and speed of neutrons emitted from Mars' surface from February 2002 to April 2003. More, slower neutrons indicate hydrogen atoms in the subsurface. To map water abundance, the neutron spectrometer team assumed all the hydrogen was in the form of water, arriving at measured abundances from 2 to above 18 percent. The lowest hydrogen abundances more likely represent water bound into minerals than as water ice, but higher amounts must represent actual ice present close enough to the surface to interact with neutrons that the neutron spectrometer could see, within a meter or two from the surface. The map is overlaid on shaded-relief MOLA topography.