Our Moon is known for being a very dry place with no water at all, except possibly for some ice at the poles. And researchers have not been able to find any in the lunar rocks brought back from the Apollo missions until recently. However, according to Scientific American, they have now found trace amounts of water in lunar volcanic glasses brought back from the Apollo missions.
Previous attempts at finding water in the lunar rocks failed because researchers could not tell whether any water detected was truly part of the original lunar material or whether they were Earth-based contaminants. Using secondary ion mass spectrometry, researchers were finally able to discover that lunar volcanic glasses contained water in a concentration of about 46 parts per million. Based on this, they estimate that the Moon once must have had water concentrations of 750 parts per million in its mantle.
It shouldn't have come as a surprise, since the Moon probably formed from the impact of a Mars-sized body with the Earth, so plenty of water must have been mixed in the impact debris. But after thinking of the Moon as a completely dry body for a long time, the news of the discovery had an impact.
The image of lunar volcanic glasses retrieved by Apollo 17 is courtesy of NASA.