Study: Moon has little water after all

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Study: Moon has little water after all

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The most exacting analysis yet of the moon's mysterious polar craters found no sign of the vast expanses of ice that scientists had hoped future lunar colonists could someday mine for precious, life-sustaining water.

The findings do not mean there is no ice in the permanently shaded craters. But if there is ice, it is probably mixed into the lunar soil in widely scattered flecks or in thin layers.

"It certainly would have been nice to find some sort of lunar skating rink, or thick layers of ice, but it looks like it's just not there," said Bruce Campbell of the Smithsonian Institution's Center for Earth and Planetary Studies.

He and colleagues at Cornell University used the mammoth radar dish at Puerto Rico's Arecibo Observatory to bounce radio waves off the craters. They probed more deeply than ever before into the craters' floors -- as far as 20 feet down in the soil.

Like earlier Earth-based radar imaging that probed only a few feet below the craters, the latest analysis showed no sign of thick ice layers. The findings appear in Thursday's issue of the journal Nature.

Campbell said the work supports the idea that any ice in the moon's polar regions is in thin layers or widely scattered crystals mixed in with the lunar soil.

That, in turn, means that moon colonists would need equipment to either sort ice particles from the soil or heat up the crater floors and collect the water vapor.

Five years ago, NASA's Lunar Prospector orbiter found tantalizing evidence that deep, dark craters at the moon's poles could harbor ice in their sunless depths.

Prospector found elevated levels of hydrogen -- a component of water -- around the poles, with the highest readings in the shaded craters. But the evidence for ice was indirect.

The moon's orientation means only about 20 percent of its shadowed polar craters can be probed by Earth-based radar, but Campbell said it is unlikely that large slabs of ice are hidden in the inaccessible areas.

Astronomers have suspected since at least the early 1960s that the moon's polar craters, miles-deep with raised rims that help keep out the slanted polar sunlight, could have trapped ice from comets over billions of years. The temperature in some craters is about minus-280 degrees F.

Alan Binder, director of the Lunar Research Institute in Tucson, Arizona, said the only way to determine for sure how much ice is on the moon is to send a human or a robot.

"You've got to go down and stick your finger in it, so to speak," he said.

NASA has no such missions planned. But a European Space Agency probe, SMART-1, should arrive in lunar orbit in early 2005 and shed more light on moon ice. (AP)

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