About 2800 kg of meteor material hits the Moon every day. Meteoroid strikes are smashing water out of the Moon’s surface.
In recent years, data from a group of spacecraft revealed trace amounts of water on the surface of the moon.
Researchers from NASA and the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, reported that streams of meteoroids striking the Moon infuse the thin lunar atmosphere with short-lived water vapor.
After a meteoroid smashes the water out to the Moon’s surface, the force of the impact coupled with the absence of an atmosphere causes it to vaporize, according to the research.
Diving in data collected by NASA’s Lunar Atmosphere and Dust Environment Explorer, researcher have found dozens of these events.
“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,” said Mehdi Benna of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland Baltimore County. Benna is the lead author of the study, published in Nature Geoscience.
LADEE was a NASA lunar exploration orbiter. The probe gathered detailed information about the structure and composition of the thin lunar atmosphere.
Impact and the Released Water
To release water, the meteoroids had to penetrate at least 3 inches (8 centimeters) below the surface. Underneath this bone-dry top layer lies a thin transition layer. And then a hydrated layer, where water molecules likely stick to bits of soil and rock, called regolith.
From the measurements of water in the exosphere, the researchers calculated that the hydrated layer has a water concentration of about 200 to 500 parts per million or about 0.02 to 0.05 percent by weight. This concentration is much drier than the driest terrestrial soil and is consistent with earlier studies. It is so dry that one would need to process more than a metric ton of regolith in order to collect 16 ounces of water.
The material on the Moon’s surface is fluffy. Therefore, even a meteoroid a fraction of an inch across can penetrate far enough to release a puff of vapor. With each impact, a small shock wave fans out and ejects water from the surrounding area.
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When a stream of meteoroids rains down on the lunar surface, the liberated water spread through the exosphere. About a third falls back down to the Moon’s surface.
The newly identified meteoroid streams, observed by LADEE, occurred on January 9, April 2, April 5 and April 9, 2014.
“The Moon doesn’t have significant amounts of H2O or OH in its atmosphere most of the time,” said Richard Elphic, the LADEE project scientist at NASA’s Ames Research Center in California’s Silicon Valley. “But when the Moon passed through one of these meteoroid streams, enough vapor was ejected for us to detect it. And then, when the event was over, the H2O or OH went away.”
“The water being lost is likely ancient,” said Mehdi Benna in a NASA press release published Monday, “either dating back to the formation of the Moon or deposited early in its history.”
The findings will help humans understand the history of lunar water – a potential resource for sustaining long term lunar operations.
Thumbnail image: Artist’s concept of the LADEE spacecraft (left) detecting water vapor from meteoroid impacts on the Moon (right). Credit: NASA/Goddard/Conceptual Image Lab