Meteor showers bring moon geysers. A lunar orbit detected additional water around the moon as the moon streamed through cosmic dust streams that can cause meteor showers on Earth.
The water was probably released from the lunar soil by tiny meteorite impacts, the planetary scientist Mehdi Benna of NASA Goddard Space The Flight Center in Greenbelt, Md., And his colleagues report on April 15 in Nature Geoscience , These random influences indicate that the water is buried all over the moon and is not isolated in frozen dark craters – and that the moon was wet for billions of years.
Lunar soil samples brought by the Apollo astronauts indicated that the moon is bone-dry. However, in the last ten years, several remote missions have found water deposits on the Moon, including signs of frozen surface water in regions of permanent shadow near the poles ( SN: 24.1
"We knew that there was water in the ground," says Benna. What the scientists did not know was how widespread water was or how long it had remained there.
Benna and colleagues used observations from the NASA spacecraft LADEE, which orbited the moon from November 2013 to April 2014 ( SN Online 18.04.14 ). The LADEE spectrometers detected dozens of sharp rises in abundance of water molecules in the exosphere of the moon, the thin atmosphere of gas molecules sticking to the moon. 29 of these measurements coincided with known space dust flows.
When the Earth passes these air streams, the dust burns in the atmosphere, producing annual meteor showers such as the Leonids and the Geminids. However, since the moon has no real atmosphere, dust particles from the same showers directly hit the surface of the moon and rain what is underneath.
Benna and colleagues calculated that only meteorites heavier than about 0.15 grams could have released the water. This means that the upper eight centimeters of the lunar soil are indeed dry – smaller impacts would have released water if one had been there. Below this dry layer is a global layer of hydrated soil with water ice attached to dust grains.
The moon is by no means muddy. Squeezing half a ton of lunar soil would hardly make a small bottle of water, says Benna. "It's not a lot of water in any way, but it's still water." And it's too much water to be on the moon recently, he says. It is possible that the moon has held at least part of this water since its formation ( SN: 15.04.17, p. 18 ).
Future studies could help to find out if and how this water could be useful to human researchers.
The finding is "plausible and certainly provocative," says planetary scientist Erik Asphaug of the University of Arizona at Tucson. "It's the kind of paper that appears well published so that we can debate it."