Moon Receives Deliveries of Water from Asteroids

October 30, 2015 | Sarah Tse

Lunar crater
Photo credit: NASA

With all the hype about water on Mars, many have forgotten that the life-giving liquid is also found on a celestial body much closer to home: the moon.

But scientists certainly haven’t forgotten, and they’ve finally figured out how water got to the moon in the first place.

SEE ALSO: It’s Official: Mars Has Liquid Water

When space exploration first began over 50 years ago, astronomers believed that the moon’s lack of an atmosphere and exposure to solar radiation kept it from harboring anything as fragile as water. But data obtained from the Lunar Prospector probe in the 1990s revealed that hidden beneath the moon’s deceptively barren facade lie surprisingly large amounts of hydrogen, which suggest the presence of water.

Scientists theorized that the moon is able to carry water despite its harsh conditions because sunlight never quite reaches the bottoms of certain craters in polar regions. These “cold traps” attract and accumulate any evaporated water that might drift from falling, icy comets.

The existence of not only traces, but considerable amounts of water in the moon’s soil was confirmed after NASA launched the Lunar Crater Observation and Sensing Satellite (LCROSS) mission in 2009. The probe crashed into the lunar surface and released a cloud of gas and dust. Spectral analysis of these particles revealed the light signatures that are emitted by water molecules. The Lunar Reconnaissance Orbiter (LRO) further confirmed these findings by generating a map of water distribution on the moon’s surface.

But there was one problem: the map didn’t match up with the locations of “cold traps” in polar craters. So scientists came up with a new theory of “lunar congelation.” This model suggests that even in regions pierced by solar rays, water ice can persist under a protective blanket of soil. To determine the source of these water deposits, Vladimir Svettsov and Valery Shuvalov from the Moscow institute of Physics and Technology constructed a computer model to simulate the fall of cosmic bodies and how much water these falls can deliver.

The model showed that icy comets normally impact the moon at such high velocities that almost all of the water would evaporate. There was no way comets could be responsible for the abundance of water on the moon. Asteroids, on the other hand, were a promising option, as the “chondrite carbonaceous” variety can carry up to 10 percent water. This water is locked into a crystal lattice of minerals and only escapes at temperatures much higher than the moon ever reaches, which means the water is likely to remain inside the asteroid in its crater.

One third of all asteroids that fall on the moon have the right velocity and angle to remain largely intact after impact. The simulation showed that a single two-kilometer sized asteroid can bring more water to the moon than billions of years of comet impacts. These deliveries of hydrated minerals could fill 2 to 4.5 percent of all lunar craters with water, even in areas exposed to the sun.

This discovery has important implications for future manned missions to the moon. Any location where water coexists with solar energy would make a great site to construct a lunar base. Having a source of water that isn’t limited to polar regions where radio communications are more difficult will expand the possibilities for lunar exploration.

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