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Isotopic enhancements of 17O and 18O from solar wind particles in the lunar regolith

Abstract

Differences in isotopic abundances between meteorites and rocks on Earth leave unclear the true composition of the gas out of which the Solar System formed1,2,3,4. The Sun should have preserved in its outer layers the original composition, and recent work has indicated that the solar wind is enriched in 16O, relative to Earth, Mars and bulk meteorites5. This suggests that self-shielding of CO due to photo-dissociation, which is a well understood process in molecular clouds, also led to evolution in the isotopic abundances in the early Solar System. Here we report measurements of oxygen isotopic abundances in lunar grains that were recently exposed to the solar wind. We find that 16O is underabundant, opposite to an earlier finding5 based on studies of ancient metal grains. Our result, however, is more difficult to understand within the context of current models, because there is no clear way to make 16O more abundant in Solar System rocks than in the Sun.

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Acknowledgements

T. Senden carried out the atomic force microscopy of ion probe pits. NASA provided lunar soil 10084,85. This work was supported by the Australian Research Council. We thank M. Thiemens, K. McKeegan and U. Wiechert for discussions, and K. Hashizume, G. Huss and A. Davis for comments and suggestions.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Correspondence to Trevor R. Ireland.

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Supplementary Notes

This file contains all Supplementary Information as follows: Supplementary Figure 1 and legend, Supplementary Figure 2 and legend, Supplementary Methods, and Supplementary Table 1. (DOC 223 kb)

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Figure 1: Oxygen-isotope depth profiles for two iron grains from lunar soil 10084.
Figure 2: Three-isotope plots of oxygen isotope compositions in lunar metal grains and lunar ilmenites.

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