Science

Meteor showers dig up water on the moon

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Meteor showers bring moon geysers. A lunar orbiter spotted extra water around the moon when the moon passed through streams of cosmic dust that can cause meteor showers on Earth.

The water was probably released from lunar soil by tiny meteorite impacts, planetary scientist Mehdi Benna of NASA Goddard Space Flight Center in Greenbelt, Md., and colleagues report April 15 in in Nature Geoscience. Those random impacts suggest water is buried all over the moon, rather than isolated in freezing dark craters — and that the moon has been wet for billions of years.

Samples of lunar soil brought back by the Apollo astronauts suggested that the moon is bone dry. But in the last decade or so, 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: 10/24/09, p. 10).

“We knew there was water in the soil,” Benna says. What scientists didnt know was how widespread that water was, or how long it had been there.

Benna and colleagues used observations from NASAs LADEE spacecraft, which orbited the moon from November 2013 to April 2014 (SN Online: 4/18/14). LADEEs spectrometers detected dozens of sharp increases in the abundance of water molecules in the moons exosphere, the tenuous atmosphere of gas molecules that clings to the moon. Twenty-nine of those measurements coincided with known streams of space dust.

When Earth passes through those streams, the dust burns up in the atmosphere, producing annual meteor showers like the Leonids and the Geminids. But because the moon has no true atmosphere, bits of dust from the same showers strike the moons surface directly, stirring up what lies beneath.

Benna and colleagues calculated that only meteorites heavier than about 0.15 grams could have released the water. That means the top eight centimeters or so of lunar soil are indeed dry — smaller impacts would have released water if any was there. Beneath that dry coating is a global layer of hydrated soil, with water ice clinging to duRead More – Source