January 10, 2011

Lunar Water Likely Came From Comets

The water on the Moon's surface predominantly originated from comets, which would have bombarded its surface early in its existence, claims a new study published in the journal Nature Geoscience.

As part of the study, astrophysicist James Greenwood from Connecticut's Wesleyan University and colleagues analyzed rock samples collected by NASA astronauts during the Apollo missions.

According to AFP reports, they were specifically looking "at variations in hydrogen isotopes in a water-loving mineral called apatite," which they say suggests three potential sources for the lunar water: "from the sub-surface lunar mantle, from protons brought by the "solar wind" of particles blasted from the Sun--and from comets."

"The isotope measurements in the apatite were similar to those previously found in three well-known comets: Hale-Bopp, Hyakutake and Halley," the French news agency added.

Joining Greenwood, a member of the Wesleyan University Department of Earth & Environmental Sciences, on the study were Shoichi Itoh, Naoya Sakamoto, and Hisayoshi Yurimoto of Japan's Hokkaido University, Paul Warren of the UCLA Department of Earth and Space Sciences, and Lawrence Taylor of the University of Tennessee Department of Earth and Planetary Sciences.

"Water plays a critical role in the evolution of planetary bodies, and determination of the amount and sources of lunar water has profound implications for our understanding of the history of the Earth-Moon system," the researchers wrote in the report, adding that lunar samples obtained through the Apollo program "were found to be devoid of indigenous water."

"The severe depletion of volatiles, including water, in lunar rock samples has long been seen as strong support for the theory that the Moon formed during a giant impact event," Greenwood and his colleagues said. "Water has now been identified in lunar volcanic glasses and apatite, but the sources of water to the Moon have not been determined. Here we report ion microprobe measurements of water and hydrogen isotopes in the hydrous mineral apatite, derived from crystalline lunar mare basalts and highlands rocks collected during the Apollo missions."

"We find significant water in apatite from both mare and highlands rocks, indicating a role for water during all phases of the Moon's magmatic history," they added. "Variations of hydrogen isotope ratios in apatite suggest sources for water in lunar rocks could come from the lunar mantle, solar wind protons and comets. We conclude that a significant delivery of cometary water to the Earth-Moon system occurred shortly after the Moon-forming impact."


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