Water on Mars May Have Piled Up as Ice Near Equator

There is plenty of evidence that water once flowed on the surface of Mars, and other evidence that points to where some of that water is now: in layers of dirty ice deposits at the poles. New radar soundings conducted by the Mars Express spacecraft suggest there might be more ice at the equator.

Thomas R. Watters of the Smithsonian Institution and colleagues analyzed radar data from the Medusae Fossae Formation, an area of rolling hills near the equator at the boundary between the Martian highlands to the south and lowlands to the north.
Not much is known about those hills, although they are thought to be deposits of volcanic ash or wind-blown sand. The radar instrument aboard Mars Express detected two echoes, one from the surface and the other from the boundary between the deposits and the underlying rock. By analyzing the time lag between the echoes, the researchers determined that the deposits were up to 1.5 miles thick.

Further analysis indicated that the deposits were probably ice containing more than the estimated 10 percent dust and sand contained in the south pole ice deposits. Even if the equatorial ice is dirty, it represents a lot of water. The researchers estimate the formation contains an amount similar to that estimated for the south pole — nearly 400,000 cubic miles of water.

http://www.nytimes.com/2007/11/06/science/space