More analysis and data are need to determine the significance of the finding and why hydrogen is in some areas and not others, Vondrak said.

Part of the answer could come Oct 9, when another craft, the Lunar Crater Observation and Sensing Satellite (LCROSS), is to crash into the moon, sending up a cloud of dust that astronomers will analyze for evidence of water and other other particles.

The two-part mission with LRO and LCROSS is just beginning, with LRO set to orbit the moon at a low altitude for at least the next year.

'The moon is starting to reveal her secrets, but some of those secrets are tantalisingly complex,' Michael Wargo, NASA's chief lunar scientist, told reporters.