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Incorporation of 16O-rich anhydrous silicates in the protolith of highly hydrated asteroid Ryugu


The abundant phyllosilicate and carbonate minerals characterizing most of the returned particles from asteroid Ryugu suggest a history of extensive aqueous alteration on its parent body, similar to the rare mineralogically altered, but chemically primitive, CI (Ivuna-type) chondrite meteorites. Particle C0009 differs mineralogically from other Ryugu particles examined so far by containing anhydrous silicates at a level of ~0.5 vol%, and thus can help shed light on the unaltered original materials that constituted Ryugu’s protolith. In situ oxygen isotope measurements of the most Mg-rich olivine and pyroxene in C0009 reveal two populations of Δ17O: −25‰ to −15‰ and −8‰ to −3‰. The former and the latter populations correlate well with silicate morphologies similar to those seen in amoeboid olivine aggregates and chondrule phenocrysts, respectively, both of which are abundant in less aqueously altered carbonaceous chondrites. This result also highlights the presence of olivine with Δ17O close to the solar value in either a CI chondrite or an asteroid with CI-chondrite characteristics, and provides strong evidence that amoeboid olivine aggregates and Mg-rich chondrules accreted into Ryugu’s protolith. Our data also raise the possibility that the protoliths of CI and other carbonaceous chondrites incorporated similar anhydrous silicates.

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Fig. 1: Representative scanning electron microscopy images of anhydrous silicates.
Fig. 2: Oxygen isotopic compositions of Mg-rich anhydrous silicates in Ryugu particle C0009.

Data availability

All analytical data related to this manuscript are provided in Tables 1 and 2 and Supplementary Table 1 and will be available via the JAXA Data ARchives and Transmission System ( after a 1 yr proprietary period. Source data are provided with this paper.


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We thank all of the scientists and engineers of the Hayabusa2 project, whose dedication and skill brought these precious particles back to Earth. This research was supported in part by the JSPS KAKENHI (under grant numbers JP18K18795 and JP18H04468 to M.I., JP20H01965 to N.T., JP18H05479 [Innovative Areas “MFS Materials Science”] to M.U., JP19H01959 to A.Y., JP18K03729 to M.K., JP21K03652 to N.I., JP17H06459 to T.U., JP19K03958 to M.A., JP17H06459 to T. Ohigashi, JP18K03830 to T.Y. and JP17H06459 and JP19H01951 to S.W.) and by the NIPR Research Project (grant number KP307 to A.Y.). K. McKeegan, E. Young and A. Brearley are thanked for discussions of the implications of the data. The UCLA ion microprobe facility is partially supported by a grant from the NSF Instrumentation and Facilities programme.

Author information

Authors and Affiliations



M.-C.L. led the project and wrote the initial draft. M-C.L., A.Y., N.T., M.I., M.U., T. Ohigashi., N.I., N.S., A.N., Y. Kodama, K.A.M., N.M. and K.Y. conducted the sample handling, preparation and mounting processes for the Ryugu grains. M.I., N.T., M.U., T. Ohigashi., K.U., K.H., I.S. and I.O. developed universal sample holders for multiple instruments. A.Y., M.K., N.I. and M.I. performed the scanning electron microscopy–energy dispersive spectroscopy analysis. A.Y. conducted the EPMA analysis and data reduction. M.-C.L., K.A.M. and N.M. carried out the oxygen isotope measurements of anhydrous silicates with secondary-ion mass spectrometry. A.N., K.Y., A.M., M.N., T.Y., T. Okada., M.A. and T.U led the JAXA curation activities for the initial characterization of the allocated Ryugu particles. S.N., T. Okada., T.S., S.T., F.T., M.Y., S.W. and Y.T. administered the project and acted as principal investigators. All authors contributed to the data interpretation, commented on the earlier versions of the manuscript and approved the final version of the manuscript for submission.

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Correspondence to Ming-Chang Liu.

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Nature Astronomy thanks Enrica Bonato, Luigi Folco and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Backscattered electron images of all anhydrous silicates measured in this work.

Backscattered electron images of all anhydrous silicates, which are categorized according to their morphology, measured in this work.

Supplementary information

Supplementary Information

Supplementary Text, Figs. 1 and 2 and Table 1.

Source data

Source Data Fig. 2

Processed oxygen isotope data of Ryugu anhydrous silicates (this study) and oxygen isotope data of CI-chondrite anhydrous silicates from the literature.

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Liu, MC., McCain, K.A., Matsuda, N. et al. Incorporation of 16O-rich anhydrous silicates in the protolith of highly hydrated asteroid Ryugu. Nat Astron 6, 1172–1177 (2022).

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