Astronomers studying the poles of the Moon with the world's largest radio telescope have failed to find evidence of water ice, raising doubts about the discovery of water ice by the Clementine spacecraft announced last year.
"We don't see anything that suggests ice," said Cornell University astronomy professor Donald Campbell. "We don't think there is any obvious evidence from the Arecibo radar images for the presence of water ice at the poles of the Moon."
Campbell, with then-graduate student Nicholas Stacy and MIT scientist Peter Ford, used the giant 300-meter (1,000-foot) radio telescope at Arecibo, Puerto Rico, to look at poles of the Moon in 1992 using the same radar wavelength, 13 cm, as the Clementine spacecraft used two years later.
The team reported that they found small patches, little more than a square kilometer (one-half square mile) in size, where the reflection of radar signals could be interpreted as ice. However, they found such patches on other areas of the moon which are sunlit and thus where ice could not exist.
Campbell and his team believe the signals are more likely caused by rough surfaces associated with impact craters, and not water ice. "Our contention is that the surface roughness is a much better candidate for the signatures we're seeing," he said.
Scientists using data collected by the Clementine spacecraft in 1994 announced last December that they had found evidence for deposits of water ice in permanently-shadowed regions of the Moon's south pole. In those areas temperatures stay cold enough to keep the ice from sublimating. Some have proposed using those deposits as a source of water for future lunar missions.
Campbell said, though, that the case was not closed on the possibility of lunar water ice. "However, neither Arecibo nor Clementine observed all the areas that are in permanent shadow and there is still the possibility that there are ice deposits in the bottoms of deep craters."
Lunar Prospector, a NASA spacecraft scheduled for launch this September, should be able to take a better look and confirm or deny the existence of lunar ice.