If space scientists hoping to send manned missions to distant planets were given one wish, many would ask for a convenient source of water outside the tug of Earth's gravity. And on March 5 they may have gotten it. Last Thursday, jubilant National Aeronautics and Space Administration researchers announced that the Lunar Prospector spacecraft had confirmed earlier indications that ice exists in potentially extractable quantities in the dark, cold regions at both of the moon's poles.

Image: Lunar Prospector "WE ARE CERTAIN!" Principal investigator Alan B. Binder announces Prospector's findings at a NASA press conference.

"We are certain we have found water," Alan B. Binder, Lunar Prospector principal investigator from the Lunar Research Institute told a packed press conference at NASA's Ames Research Center. Based on the present preliminary data, the researchers estimate that anywhere from 11 to 330 million tons of frozen water are mixed in the lunar soil, or regolith. The water appears to be distributed over 3,600 to 18,000 square miles across the northern pole, and an additional 1,800 to 7,200 square miles in the southern polar region. Moreover, the concentration of water near the South pole appears to be twice as great in the northern region.

If the water can be mined, it will become an enabling factor for establishing permanent or semi-permanent moon bases and, possibly, for setting up a staging area for future manned missions to Mars. The water could be used for domestic purposes, but also broken into its component hydrogen and oxygen to provide breathable air. The two elements could also be recombined as fuel for spacecraft or machinery on the base itself. "This is a tremendous resource for further exploration," said Binder. Indeed, the NASA scientists estimate that the supply of water would reduce the cost of a mission to Mars by about 50 percent.

Image: NASA CRATER LAKES. Clementine images of the moon's South polar region taken during one lunar day reveal deep craters that are shaded from sunlight.

The first evidence of water on the moon was sent back by a joint Defense Department-NASA spacecraft called Clementine in 1994. Clementine used radar to detect the signature of water in the permanently-shadowed South polar region, which scientists thought was the most likely place to look for water. Although tantalizing, these data were not conclusive.

Lunar Prospector, which was launched on January 6 as part of NASA's low budget Discovery program to study the composition of the moon, has apparently put doubts to rest in the first weeks of its planned two-year mission. In the following months, Prospector will continue to send back more detailed data, eventually dropping from its present orbit 62 miles above the moon's surface to a mere six miles for an even closer look.

Scientists think that impacting comets delivered any water that now exists on the moon. "The moon was born hot," said Binder, "all the atmosphere and water boiled away." Even the water in a comet striking the lighted regions of the moon would quickly evaporate in the daytime temperatures, which exceed 250 Fahrenheit. The only places in which water molecules could remain is in the shade of craters and perpetually dark areas of the moon, where temperatures stay at a chilling minus 280 Fahrenheit.

The new findings, made by Prospector's neutron spectrometer, confirm that water is trapped in the frigid regions of the moon. Neutrons from the solar wind continually bombard the moon. But if a neutron collides with an atom of hydrogen, it looses speed.