If you have seen pictures of the Moon, you see a giant ball of dust with astronaut footprints etched into the surface - but information garnered from missions such as NASA's 2009 Lunar CRater Observation and Sensing Satellite (L-CROSS) lunar-impact probe, along with more modern scanning technologies and precise measurements, are changing the perception it is all dry. 

 As little as five years ago, no one had detected water in the samples returned from the Moon. The advancement of instrumentation, such as secondary ion mass spectrometry and Fourier transform infrared spectroscopy, has made it possible to detect tiny, but measurable, amounts of water in the mineral grains from Apollo samples.

In a new paper, researchers show that they have detected significant amounts of water in the samples of the lunar highland upper crust obtained during the Apollo missions. The lunar highlands are thought to represent the original crust, crystallized from a mostly molten early Moon that is called the lunar magma ocean.

Their findings indicate that the early Moon was not only wet, but also the water that was there was not substantially lost during the Moon's formation. This new evidence seems to contradict the predominant lunar formation theory — that the Moon was formed from debris generated during a giant impact between Earth and another planetary body, approximately the size of Mars. According to Hejiu Hui, postdoctoral research associate at the University of Notre Dame<, "The presence of water in the early Moon needs to be reconciled with the favored formation scenario that had been supported by the volatile elements and isotopes in the samples, such as Zinc.

"It's not 'liquid' water that was measured during these studies but hydroxyl groups [developed from water that did exist in the lunar magma ocean] that was distributed within mineral grain. We are able to detect those hydroxyl groups in the crystalline structure of the Apollo samples."

The hydroxyl groups the team detected are evidence that the lunar interior contained significant water during the Moon's early molten state, before the crust solidified, and that they may have played a key role in the development of lunar basalts.

"The presence of water," says Hui, "could imply a more prolonged solidification of the lunar magma ocean than the once popular anhydrous moon scenario suggests."

Citation: Hejiu Hui, Anne H. Peslier, Youxue Zhang&Clive R. Neal, 'Water in lunar anorthosites and evidence for a wet early Moon', Nature Geoscience (2013) doi:10.1038/ngeo1735