When meteorites slam into the moon, they undoubtedly kick up a little dust. Now, a new study suggests they also shake loose quite a bit of water—something on the order of 200 tons each year.
Planetary scientists were tipped to the leaching after reviewing sensor data from a moon-orbiting probe. Between November 2013 and April 2014, the Lunar Atmosphere and Dust Environment Explorer recorded occasional spikes in the numbers of particles, including water molecules, that were lofted off the moon. Of the 39 spikes, 29 occurred within 48 hours of the moon and Earth passing through annual meteor showers that are broad enough to hit both bodies. In general, the stronger the meteor stream, the more particles were tossed into space from the moon, the researchers report today in Nature Geoscience.
The amounts of water detected by the sensors were far too high to have come from the meteorites themselves or from vaporized soil, the researchers suggest. Instead, they propose that most of that water was probably shaken loose from lunar soil grains near the meteorites’ impact sites. Over the course of a year, meteorites probably set free about 300 metric tons of water from the moon’s soil. Whereas about one-third of that water ends up elsewhere on the moon, including permanently shadowed areas near the lunar poles, the remainder—about 200 tons—is permanently lost to space.
The team’s findings suggest lunar soil between a desiccated surface layer 8 centimeters thick to a depth of 3 meters contains between 200 and 500 parts per million of water—and that the water may be more readily extracted from the soil than previously presumed.