In addition, there were squiggles in the data that indicated other molecules, possibly carbon dioxide, sulfur dioxide, methane or more complex carbon-based molecules. “All of those are possibilities,” Dr. Colaprete said, “but we really need to do the work to see which ones work best.”

Remaining in perpetual darkness like other craters near the lunar poles, the bottom of Cabeus is a frigid minus 365 degrees Fahrenheit, cold enough that anything at the bottom of such craters never leaves. These craters are “really like the dusty attic of the solar system,” said Michael Wargo, the chief lunar scientist at NASA headquarters.

The Moon was once thought to be dry. Then came hints of ice in the polar craters. In September, scientists reported an unexpected finding that most of the surface, not just the polar regions, might be covered with a thin veneer of water.

The Lcross scientists said it was not clear how all the different readings of water related to one another, if at all.

The deposits in the lunar craters may be as informative about the Moon as ice cores from Earth’s polar regions are about the planet’s past climates. Scientists want to know the source and history of whatever water they find. It could have come from the impacts of comets, for instance, or from within the Moon.

“Now that we know that water is there, thanks to Lcross, we can begin in earnest to go to this next set of questions,” said Gregory T. Delory of the University of California, Berkeley.

Dr. Delory said the findings of Lcross and other spacecraft were “painting a really surprising new picture of the Moon; rather than a dead and unchanging world, it could be in fact a very dynamic and interesting one.”