By Sean Henahan, Access Excellence

WASHINGTON, D.C. (Dec.3, 1996) When man first walked on the moon 27 years ago not a single molecule of water was found. Now a US satellite has sent back information suggesting they may not have been looking in the right place.

Graphic: Orbital geometry of the Clementine bistatic radar experiment.

The Clementine satellite began its moon-mapping mission two and a half years ago. Since then is has mapped the lunar surface at a number of resolutions and wavelengths. A radar analysis of the dark side of the moon revealed an anomaly that researchers can best be explained as a small lake of frozen water. The suspected water is located in the permanently shadowed regions of the lunar south pole.

The researchers speculate that the ice may have been deposited by a comet and/or meteoroid impacts. Any water that found its way into permanently shaded areas would be frozen in place at a continuous temperature of minus 375 degrees Fahrenheit.

By coincidence, the news of water on moon comes at a time when NASA is getting ready to launch another unmanned mission to the Moon, one of the goals of which is to look for water. The Lunar Prospector will fly in a low polar orbit, where it will map minerals on the surface, catch signs of seismic activity and hunt for water.

Clementine's information is based on radar surveys. The Lunar Prospector will have much more advanced equipment on board, including a neutron spectrometer that can detect faint traces of water ice. It will examine the poles to 80 degrees latitude with high sensitivity to the presence of hydrogen.

When high-energy cosmic rays slam into the moon's surface, various particles spray outward in response, including neutrons traveling at a variety of speeds. If water is present, it slows some of the neutrons, creating a deficit of ones traveling at medium speeds. The spectrometer will measure the speed, or energy, of all the neutrons it encounters; fewer medium-speed neutrons compared to the number of fast and slow neutrons is a unique signature for the presence of water.

"If there is water on the moon within about one meter of the surface, we will find it," said Bill Feldman, of Los Alamos Laboratories. And if Prospector finds a large enough supply of water, human colonization of the moon may be feasible.

"We'll know within a month of Prospector's deployment in orbit," said Feldman. "If we see water, I suspect the land rush is on."

In addition to providing moon explorers with a source of drinking water, the moon water could also be used to generate hydrogen-based rocket fuel, researchers note.

The research was published in the 29 November 1996 issue of Science.