This set of graphs shows variation in the amount and the depth of water detected beneath NASA's Mars rover Curiosity by use of the rover's Dynamic Albedo of Neutrons (DAN) instrument at different points along the distance the rover has driven, in meters.
DAN detects even very small amounts of water in the ground beneath the rover, primarily water bound into the crystal structure of hydrated minerals. The bottom graph indicates that the water content of the top 2 feet (60 centimeters) of the ground at points in the "Yellowknife Bay" area where DAN has taken measurements is estimated at about 3 percent.
Image Credit: NASA/JPL-Caltech/Russian Space Research Institute
Browse Image | Medium Image | Full Res Image (NASA's Planetary Photojournal)