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Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon


Water plays a critical role in the evolution of planetary bodies1, and determination of the amount and sources of lunar water has profound implications for our understanding of the history of the Earth–Moon system. During the Apollo programme, the lunar samples were found to be devoid of indigenous water2,3. The severe depletion of volatiles, including water, in lunar rock samples4 has long been seen as strong support for the theory that the Moon formed during a giant impact event5. Water has now been identified in lunar volcanic glasses6 and apatite7,8,9, 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. 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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Figure 1: Backscatter electron image and SCAPS 1H image of apatite grain 5 of 10044,12.
Figure 2: δD(‰) versus H2O (wt.%) of lunar apatite measured in this study.
Figure 3: δD plot of the solar system.


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We thank F. M. McCubbin and F. Robert for constructive reviews, M. Gilmore and W. Herbst for comments on an earlier version of this manuscript, M. Rutherford and A. Basilevsky for discussion, G. Olack and J. Eckert for technical assistance, and Wesleyan University (J.P.G.) and Monkasho (H.Y.) for support.

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J.P.G., S.I., N.S. and H.Y. carried out all ion microscopy. J.P.G. conducted all electron microscopy and measurements of water and D/H in apatite standards using continuous-flow mass spectrometry. All authors contributed to writing of the manuscript.

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Correspondence to James P. Greenwood.

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The authors declare no competing financial interests.

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Greenwood, J., Itoh, S., Sakamoto, N. et al. Hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the Moon. Nature Geosci 4, 79–82 (2011).

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