ON THE ROCKS

As cosmic real estate goes, few places are less desirable than the moon. Last week, however, the bleak world started to look more hospitable when scientists announced that it is home to a decidedly terrestrial feature: a mammoth field of ice.

For all the visits spacecraft and astronauts have made to the moon, they have limited their explorations to roughly equatorial areas, largely neglecting the polar regions. In 1994 NASA and the Pentagon launched a probe into a vertical lunar orbit that would reach those extreme latitudes.

One of the first things they looked for was water. Though moisture elsewhere on the moon would sizzle away under the unfiltered sun, the poles are different. Since the inclination of the moon is nearly upright, sunlight strikes it obliquely, plunging polar craters into darkness. Any water at the bottom of such depressions would flash-freeze at temperatures reaching -387[degrees] F.

When the spacecraft trained its radio scanners on the lunar south pole's deep Aitkin Basin, the reflected signal indicated that it had spotted just such an ice deposit. "If you collected all the ice scattered across that basin," said Dwight Dunston, a mission director, when the discovery was announced last week, "it would form a lake 16 ft. deep and four football fields around."

No one is certain where the water came from, though a collision with an icy comet is likely. Just as important as the origin of the ice is its future. "Settlers could break the water into oxygen and hydrogen and turn them into rocket fuel and air," suggests Dunston. And as for the possibility of ice-dwelling organisms? Not likely. Water may help sustain life, but at nearly 400[degrees] below, it couldn't get started in the first place.

--By Jeffrey Kluger. With reporting by Dick Thompson/Washington