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

Journal name:
Nature Geoscience
Volume:
4,
Pages:
79–82
Year published:
DOI:
doi:10.1038/ngeo1050
Received
Accepted
Published online

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.

At a glance

Figures

  1. Backscatter electron image and SCAPS 1H image of apatite grain 5 of 10044,12.
    Figure 1: Backscatter electron image and SCAPS 1H image of apatite grain 5 of 10044,12.

    a, Backscatter electron image. Apatite (Ap) is texturally associated with many late-stage crystallization minerals, such as fayalite (Fa), pyroxferroite (Pyf), K–Ba-rich feldspar (KBa), hedenbergite (Hd), iron sulphide (FeS), a silica phase (Si), and finely intergrown mesostasis (Meso) composed of plagioclase (Pg) and silica. The location of the SCAPS image is outlined by the white rectangle. b, SCAPS 1H image of apatite, mesostasis, pyroxferroite, K–Ba-rich feldspar and cracks. Cracks are high in hydrogen (and are white in the image). The D/H of cracks are low and indicative of terrestrial adsorbed water (see Supplementary Table S5). A K–Ba-rich feldspar grain included in the apatite is cut by a crack containing high hydrogen. The apatite grain has more hydrogen than the included K–Ba-rich feldspar or the pyroxferroite and mesostasis that the apatite is in contact with in this image.

  2. [delta]D([permil]) versus H2O (wt.%) of lunar apatite measured in this study.
    Figure 2: δD(‰) versus H2O (wt.%) of lunar apatite measured in this study.

    Three apatite grains are essentially dry (12040,211; 12013,148; 14305,94), and two of these have δD that are difficult to distinguish from terrestrial water. The error bars are 2σ.

  3. [delta]D plot of the solar system.
    Figure 3: δD plot of the solar system.

    D/H of water is shown, with the exception of the outer planets and the protosolar estimate, which are H2. The venusian atmosphere and interplanetary dust particles (IDPs) have extreme D-enrichment owing to escape of water from the venusian atmosphere and interstellar water, respectively. Several chondrite data in the literature overlap with the lunar data (excluding 14053), but most do not14. Mean δD for bulk carbonaceous chondrite water and ordinary chondrite chondrule and clay water are shown here. Comet data seem to have a similar range to the high-δD lunar analyses. Sources of data (ref. 14 and references therein, refs 15, 16, and J.P.G., unpublished data for Mars OH).

References

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Author information

Affiliations

  1. Department of Earth & Environmental Sciences, Wesleyan University, 265 Church Street, Middletown, Connecticut 06459, USA

    • James P. Greenwood
  2. Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan

    • Shoichi Itoh,
    • Naoya Sakamoto &
    • Hisayoshi Yurimoto
  3. Department of Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, California 90095-1567, USA

    • Paul Warren
  4. Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, 1412 Circle Drive, Knoxville, Tennessee 37996-1410, USA

    • Lawrence Taylor

Contributions

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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