Mars today is a polar desert. Orbiting 1.5 times farther from the Sun than Earth, Mars intercepts only 44% of the solar energy received by our planet. Martian gravity, about 1/3 of Earth's, can hold only a very thin atmosphere, which traps little solar heat. The temperature rarely rises above freezing anywhere on the planet. The low atmospheric pressure prevents liquid water from remaining on the surface. It seems that a discussion of water on Mars might be short and not very interesting.

But … things are not always as they seem, nor are things today the same as they have always been. Mars does have water - albeit frozen - in the air, on the surface, and buried deep underground. Also, strong evidence points to an earlier time when great floods