That interpretation has received widespread media coverage because the availability of ice would increase the feasibility of establishing a human base on the Moon by providing a ready source of water, oxygen and hydrogen. So far the evidence for lunar ice has been indirect.

On July 31, however, NASA intends to crash the Lunar Prospector spacecraft into a south polar crater to produce a plume of material. Mission scientists claim that if the plume contains traces of water and hydroxyl ions it will prove the existence of lunar ice

Unfortunately, the crash will not be a definitive test, assert Von R. Eshleman, professor emeritus of electrical engineering, and George A. Parks, professor of geological and environmental sciences, in a letter that appears in the July 23 issue of the journal Science.

Eshleman and Parks argue that if ice ever did exist in the Moon's polar shadows, it may have reacted long ago with the dust that covers the lunar surface (a material that strongly resembles Portland cement) to form a substance that resembles the hydrous (water containing) minerals in concrete paste.

The lunar dust is anhydrous (without water in any form), but is capable of absorbing large amounts of water and chemically incorporating the hydrogen and oxygen atoms into the mineral crystals.

The two researchers further argue that the presence of such a concrete paste provides a better explanation than does water ice for the observations of the two lunar satellites, the returns from Earth-based radar and the observations and experiments conducted during the Apollo program.

Finally, the two researchers predict that, if they are correct and the south polar crater is covered with concrete paste instead of water ice, the crash of the Lunar Prospector could melt the paste to produce a plume of water vapor and hydroxyl ions even though water was not previously present.