Abstract
The samples returned from asteroid Ryugu were collected both at its surface and at its subsurface by Hayabusa2 and can, thus, provide information on the space weathering of C-type asteroids at different depths without terrestrial contamination. The near-infrared hyperspectral microscope MicrOmega gathered data on the –OH feature at ~2.7 μm for 177 individual grains from the two collection sites. Here, through a spectral analysis of these data, we show that the position of the band peak can be used as an indicator of the degree of space weathering. Most subsurficial grains do not present space weathering features, indicating that Ryugu’s subsurface layers have never been exposed to the interplanetary medium. Moreover, the ~2.7 μm feature for the Ryugu samples is narrower than that observed for CI chondrites, which are the closest meteorite analogues to Ryugu, suggesting that these contain more absorbed molecular water than Ryugu due to terrestrial aqueous contamination. We conclude that Ryugu samples should be considered as a reference for the primordial water abundance within primitive bodies.
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Data availability
The average spectrum of each grain assessed in this study is available from the Ryugu Sample Database System (JAXA) at https://darts.isas.jaxa.jp/curation/hayabusa2/. Source data are provided with this paper.
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Acknowledgements
We thank the whole Hayabusa2 team for their scientific and technical contributions to this successful mission. We thank the National Centre for Space Studies, which is the French space agency, for its support. T.Y. received support from the Japan Society for the Promotion of Science, grant number JP18K03830. We warmly thank P. Beck and D. Takir for providing us with near-infrared spectra of carbonaceous chondrites.
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R.B., C.P., J.-P.B., A.N., V.H., K.H., D.L., L.R., K.Y., T.O., T.Y., T.U., M.A., T.S., S.T., S.N., Y.T. and S.W. conceived and designed the experiments. T.L.P.-J., R.B., C.P., J.-P.B., A.N., K.H., C.L., D.L., L.R., K.Y., T.O., T.Y., Y.H., K.K., A.M., K.N. and M.N. performed the experiments. T.L.P.-J., R.B., C.P., J.-P.B., A.N., C.L., D.L., L.R., D.B., F.P., A.A.-T., J.C. and Y.L. analysed the data. T.L.P.-J., R.B., C.P., A.N., V.H., K.H., C.L., D.L., L.R. and K.Y. contributed materials and analysis tools. T.L.P.-J., R.B., C.P., J.-P.B., A.N., C.L., L.R., D.B., F.P. and T.O. wrote, discussed and commented on the paper.
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Supplementary Figs. 1–17 and Tables 1–4.
Source data
Source Data Fig. 2
Table of peak positions and band depths for all grains assessed in this study.
Source Data Fig. 4
Table of peak positions and band depths for all grains assessed in this study.
Source Data Fig. 5
Table of peak positions and band depths for all grains assessed in this study.
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Le Pivert-Jolivet, T., Brunetto, R., Pilorget, C. et al. Space weathering record and pristine state of Ryugu samples from MicrOmega spectral analysis. Nat Astron 7, 1445–1453 (2023). https://doi.org/10.1038/s41550-023-02092-9
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DOI: https://doi.org/10.1038/s41550-023-02092-9
