Scientists Identify Source of the Moon's Water

May 31, 2016

The Moon contains small but potentially significant amounts of water. Rock samples collected by the Apollo astronauts suggest the interior of the Moon contains 10 to 300 parts per million water. Although that is not a lot of water, when it is vented to the surface by volcanic and impact cratering events, it may have been concentrated in permanently shadowed and very cold regions on the lunar surface. Scientists are intrigued by the source of that water and when the Moon acquired it. Did the material come from asteroids, comets, or some other source? Lurking in the answer to that question may be additional clues about how the solar system formed, how the Moon accreted, and how impact bombardment affected the Moon when it was transitioning from a molten mass to a planetary body with a substantially solid crust. Credit: LPI/David A. Kring.

According to a new study published in Nature Communications, most of the water inside the Moon was delivered by asteroids (not comets) during the early evolution of the Moon, approximately 4.5–4.3 billion years ago.

In the Apollo era, the Moon was often described as being devoid of water. As analytical techniques improved, scientists realized that water resided in the lunar interior, but in quantities that had simply been impossible to detect when lunar samples were originally returned to Earth. The discovery of water in lunar samples prompted a new question:   What was the source of the Moon’s water?

In the current study, an international science team compared the chemical and isotopic composition of lunar volatiles (including water) with those of volatile materials in comets and meteoritic samples of asteroids. They then calculated the proportion of water that could have been delivered by those two populations of objects. Their results indicate that most (>80%) of the water in the lunar interior was derived from asteroids that are similar to carbonaceous chondritic meteorites. That water was delivered when the Moon was still surrounded by a magma ocean and before a massive crust (now seen as the bright white highlands of the Moon) prevented impacting objects from delivering significant amounts of material to the lunar interior. A similar delivery of water to Earth would have been occurring within this same interval of time.

These results were derived by an interdisciplinary team with extensive experience studying both the Moon and meteoritic samples of impacting asteroids. The lead author of the paper is Jessica Barnes (The Open University, Milton Keynes). Co-authors are David Kring [Lunar and Planetary Institute (LPI), Houston], Romain Tartèse (Muséum National d'Histoire Naturelle, Paris), Ian Franchi (The Open University), Mahesh Anand (The Open University), and Sara Russell (The Natural History Museum, London).

Barnes, is a former graduate student intern in the Center for Lunar Science and Exploration (CLSE) Lunar Exploration Summer Intern Program, is currently a CLSE postdoctoral international partner, and is an incoming postdoctoral researcher at the NASA Johnson Space Center and the LPI, which is managed by the Universities Space Research Association (USRA) for NASA.

Kring’s portion of the work was supported at the LPI by cooperative agreements to USRA from NASA’s Planetary Science Division and NASA’s Solar System Exploration Research Virtual Institute.

For more information, visit

An Asteroidal Origin for Water in the Moon (article in Nature Communications, DOI:  10.1038/ncomms11684)

Center for Lunar Science and Exploration

What Really Caused Water Inside the Moon

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Last updated June 20, 2016