The Moon’s Water Comes From the Sun

An image of water-filled debris ejected from Cabeus crater about 20 seconds after the 2009 LCROSS impact. Courtesy of Science/AAAS.

Comets? Asteroids? The Earth? The origins of water now known to exist within the Moon’s soil — thanks to recent observations by various lunar satellites and the impact of the LCROSS mission’s Centaur rocket in 2009 — has been an ongoing puzzle for scientists. Now, new research supports that the source of at least some of the Moon’s water is the Sun, with the answer blowing in the solar wind.

Spectroscopy research conducted on Apollo samples by a team from the University of Tennessee, University of Michigan and Caltech has revealed “significant amounts” of hydroxyl within microscopic glass particles found inside lunar soil, the results of micrometeorite impacts.

According to the research team, the hydroxyl “water” within the lunar glass was likely created by interactions with protons and hydrogen ions from the solar wind.

“We found that the ‘water’ component, the hydroxyl, in the lunar regolith is mostly from solar wind implantation of protons, which locally combined with oxygen to form hydroxyls that moved into the interior of glasses by impact melting,” said Youxue Zhang, Professor of Geological Sciences at the University of Michigan.

Hydroxyl is the pairing of a single oxygen atom to a single hydrogen atom (OH). Each molecule of water contains two hydroxyl groups.

Although such glass particles are widespread on the surface of the Moon — the researchers studied samples returned from Apollo 11, Apollo 16 and Apollo 17 missions — the water in hydroxyl form is not something that could be easily used by future lunar explorers. Still, the findings suggest that solar wind-derived hydroxyl may also exist on the surface of other airless worlds, like Mercury, Vesta or Eros… especially within permanently-shadowed craters and depressions.

“These planetary bodies have very different environments, but all have the potential to produce water,” said Yang Liu, University of Tennessee scientist and lead author of the team’s paper.

The discovery of hydroxyl within lunar glasses presents an “unanticipated, abundant reservoir” of water on the Moon, and possibly throughout the entire Solar System.

The study was published online Sunday in the journal Nature Geoscience.

Source: University of Michigan news release.

Inset image: a grain of lunar agglutinate glass from samples returned by Apollo astronauts (Yang Liu)