After analyzing data from a radar device aboard last year's Indian Chandrayaan-1 mission to the Moon, NASA scientists have found what they estimate to be 600 million metric tons of water ice in craters around the Moon's north pole. "Numerous craters near the poles of the Moon have interiors that are in permanent sun shadow. These areas are very cold and water ice is stable there essentially indefinitely. Fresh craters show high degrees of surface roughness (high circular polarization ratio) both inside and outside the crater rim, caused by sharp rocks and block fields that are distributed over the entire crater area. However, Mini-SAR has found craters near the north pole that have high CPR inside, but not outside their rims. This relation suggests that the high CPR is not caused by roughness, but by some material that is restricted within the interiors of these craters. We interpret this relation as consistent with water ice present in these craters. The ice must be relatively pure and at least a couple of meters thick to give this signature."