X - The Ten Instruments Mars Rover Curiosity Carries : Dynamic Albedo of Neutrons
Dynamic Albedo of Neutrons
Even if Curiosity doesn't, say, run into a puddle, there are still ways for it to discover water on Mars. Cosmic rays constantly hit the planet's surface, knocking neutrons out of orbit. Hydrogen atoms in water or ice will slow those neutrons down, and that can be detected.
A pulsing neutron generator called the Dynamic Albedo of Neutrons (DAN) can detect water content as small as one-tenth of 1 percent. DAN will send a beam of neutrons into the surface, three to six feet into the ground; if it detects a large amount of slower neutrons, that's decent evidence there's water underneath.