Big Splash: How Water on the Moon Was Found

Sept. 24, 2009 — -- Water on the moon? If you had asked almost any space scientist about it after Apollo 11, you would have gotten nowhere.

The moon was dry as dust -- even more so -- they would have told you. For sure, the moon was probably pummeled with comets -- which are largely ice -- billions of years ago, when the solar system was young and filled with debris. But on an airless world, baked by the sun, any water would probably have vaporized and escaped into space.

"It was a question we thought we didn't have to address," said Carle Pieters, a space scientist at Brown University, in an interview with ABCNews.com. She is a member of the team whose work is making headlines around the world today.

Since the 1990s, scientists have been reporting indirect evidence of water, or at least its chemical components, from readings taken by passing spacecraft. The prevailing theory has been that there may be pockets of ice, mixed with soil in craters near the lunar south pole, where the sun never shines and the ice is always hundreds of degrees below zero.

But now Pieters and her colleagues have delivered a surprise. They say they found evidence of water -- in small concentrations, but enough to add up to billions of gallons -- virtually all over the lunar surface.

The data came from three different robot space probes:

One was India's Chandrayaan-1, which has been orbiting the moon since late last year.

An American ship, called Deep Impact, has mostly been used to examine comets, but pointed its instruments at the moon in June.

And NASA's Cassini spacecraft, now orbiting Saturn, took some long-distance measurements of the moon on the way out from Earth in 1999 -- though nobody thought to analyze the data at the time.