Oct 21, 2010  -- Water on the moon? Scientists used to think it was as dry as, well, lunar dust.

But after a year of analysis NASA today announced that its LCROSS lunar-impact probe mission found up to a billion gallons of water ice in the floor of a permanently-shadowed crater near the moon's south pole.

That's enough, said researchers, to fill 1,500 Olympic-size swimming pools, all from one crater.

If there is ice there, it probably exists in other places on the moon as well. They also found silver, mercury, carbon monoxide and ammonia.

LCROSS was an empty rocket stage that was deliberately crashed into the moon last year, while a small satellite trailing it took chemical measurements of what it kicked up. Its target, a crater called Cabeus, was chosen because it is so deep that sunlight never reaches the bottom -- and any ice there, mixed in the soil, would never have a chance to vaporize. The ice might have remained frozen there for billions of years.

"To our surprise, some of the permanently shadowed regions had no water, but some of the areas that receive sunlight occasionally did have water," said William Boynton of the University of Arizona, a member of the research team.

The LCROSS researchers had already announced preliminary findings last November -- about a third less water than they reported today -- and refined their numbers in the months since. Their conclusions appear today in the journal Science.

Finding large amounts of water on the moon could be important, not just for science, but for future exploration by astronauts. Water, essential for human survival, would be heavy and expensive for spacecraft to bring from earth. But if astronauts land near ice deposits, as NASA has long hoped, they could, in effect, live off the land.

Water on the Moon: A Billion Gallons in One Crater

The ice could be melted and purified for drinking and cooling of spacecraft systems -- and beyond that, it could also be broken down into its components, hydrogen and oxygen. Hydrogen could be used as rocket fuel; oxygen could be used for breathing.

"This place looks like it's a treasure chest of elements, of compounds that have been released all over the moon and they've been put in this bucket in the permanent shadows," said planetary geologist Peter Schultz of Brown University in Rhode Island in a statement.

How much water did they actually find? The researchers said the satellite measured about 41 gallons in the debris from the 60-foot crater gouged out by the crashing rocket. Since the ice was mixed in with rock and dust, its chemical signature -- H2O -- was mixed in with the myriad minerals to be found in lunar soil.

Some of those other minerals were less than welcome to the researchers. Mercury, in particular, is toxic, so the idea of astronauts simply melting the ice for personal use becomes more complicated. And the scientists said not to get excited about the silver they found; it's hardly enough to be worth mining.

There is no saying whether astronauts will get to use that ice any time soon. The Obama administration early this year canceled the Constellation project, which had been proposed by President George W. Bush, to return astronauts to the moon and eventually send them on to Mars. They will still go to Mars, someday, but the moon plans, when given another look, appeared unaffordable.

But scientists' image of the moon has changed since the Apollo astronauts came home. Anthony Colaprete, the chief mission scientist, said Cabeus crater was like an "oasis in a lunar desert."