The meteor shower is carried by local geysers. The moon's orbiter observed additional water around the moon when the moon passed through the streams of cosmic dust that could cause meteor rain on Earth.
Water is probably released from the moon's earth with small meteor strokes, planetary scientist Mehdi Benn of NASA's Space Flight Center in Greenbelt, and colleagues reported on April 15 Nature Geoscience, These random influences suggest that water is buried throughout the Moon, not isolated in frozen dark craters – and that the moon has been milled for billions of years.
Samples of lunar soil brought by Apollo astronauts indicate that Moon is a dry bone. But in the last decade, several distant missions have found water deposits in the moon, including frozen surface water signs in areas of permanent shadows near poles (SN: 10/24/09, p. 10).
"We knew there was water in the ground," says Benna. What the scientists did not know was how widespread the water was or how long it was there.
Barrels and colleagues used observations from NASA's spacecraft LADEE, which spanned around the month from November 2013 to April 2014 (SN Online: 4/18/14). LADEE's spectrometers have found dozens of sharp increases in the abundance of water molecules in the moon's exosphere, the weak atmosphere of the molecules that hold the Moon. Twenty-nine of these measurements coincided with the familiar streams of space dust.
When the Earth passes through these streams, dust sparks into the atmosphere, creating annual meteor rains such as Leonid and Geminid. But since the moon does not have a true atmosphere, dust bits from the same shower directly impact the Moon's surface, encouraging what's underneath.
Barrels and colleagues calculated that meteorites only weighing about 0.15 grams could release water. This means that the top of eight inches or so of the lunar soil is really dry – fewer shots would release water if it was. Below this dry coating is a global layer of hydrated soil with a water ledge holding grain dust.
But the moon is not moist. Squeezing half a ton of lunar soil would hardly bring a small bottle of water, says Benna. "There is not much water to any extent, but it is still water." And that's too much water that he recently arrived at the Moon, he says. The moon may have retained at least part of that water since its formation (SN: 4/15/17, p. 18).
Future studies can help determine whether and how this water could be useful to human researchers.
This finding is "convincing and certainly provocative," says planetary scientist Erik Asphaug from Arizona University in Tucson. "It's a kind of paper that is well-publicized so we can discuss it."