Water content of Moon remains uncertain

BBC : Once thought bone dry, the Moon is now thought to have had water—but how much is yet to be determined. Traces of hydroxyl-rich apatite in lunar rocks had led researchers a few years ago to believe there could have been considerable water—enough, if brought to the surface, to cover the Moon with a layer of liquid water one meter deep. New findings dispute that, however. According to simulations, the concentration of OH in lunar apatite is not proportional to the amount of water in lunar magma; rather, it depends on crystallization conditions and on the presence of another volatile element, chlorine. The new findings are consistent with the scenario that the Moon was formed when a Mars-sized impactor slammed into Earth. Any water in the collision fragments would have boiled away by the time they coalesced to form the Moon.