April 15 (UPI) -- The small space rocks that regularly pepper the moon are squeezing water from the lunar surface, perfuming the thin lunar atmosphere with ephemeral vapors.
Computer models previously predicted streams of meteoroids ejecting water from the moon's surface, but until now, the phenomenon hadn't been directly observed.
When scientists surveyed data collected by NASA's Lunar Atmosphere and Dust Environment Explorer, a lunar orbiter, they were able to connect brief spikes in atmospheric water vapor levels with meteoroid streams.
"We traced most of these events to known meteoroid streams, but the really surprising part is that we also found evidence of four meteoroid streams that were previously undiscovered," Mehdi Benna, scientist at NASA's Goddard Space Flight Center, said in a news release.
Benna and his colleagues described their discovery this week in the journal Nature Geoscience.
Scientists have previously found evidence of water inside the moon. Researchers have mapped the presence of water in the lunar soil, as well as captured images of ice on the surface of the lunar poles. Hydroxyl, a highly reactive relative of H2O, is also present on the moon. The science of how water got to the moon and how much there is, however, remains unsettled.
What water is present on the moon mostly remains locked up in ice form and trapped underground. As a result, the lunar atmosphere is usually without water vapor. The LADEE data, however, showed tiny impacts can briefly free up some of the moon's water.
"When the moon passed through one of these meteoroid streams, enough vapor was ejected for us to detect it," said Richard Elphic, the LADEE project scientist at NASA's Ames Research Center. "And then, when the event was over, the H2O or OH went away."
The lunar surface is dry, but scientists predict a layer of hydrated sediment lies just beneath the surface. To free up the buried water, researchers estimated the meteoroid stream would have to penetrate at least three inches.
As the moon passes through a meteoroid stream, the tiny impacts generate shock waves that expel puffs of vapor into the lunar atmosphere, or exosphere, the thin envelope of gas that surrounds the satellite.
"We know that some of the water must be coming from the Moon, because the mass of water being released is greater than the water mass within the meteoroids coming in," said Dana Hurley, a researcher at the Johns Hopkins University Applied Physics Laboratory.
NASA scientists hope future lunar missions will uncover new details about the ratio of H20 to OH, as well as offer insights into the origins of the moon's ancient water reserves.