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Hydrothermal fluid activity on asteroid Itokawa


Carbonaceous chondrites contain widespread mineralogical evidence for water–rock interactions, indicating that the C-type asteroids from which they are derived had active hydrothermal systems. In comparison, ordinary chondrites contain secondary minerals that are predominantly anhydrous, suggesting that their parent S-type asteroids were relatively dry. The returned particles from the Hayabusa Mission allow us to probe directly the alteration history of S-type asteroid Itokawa. Here we report nanometre-sized NaCl crystals identified in the interior of an Itokawa particle. These crystals are intimately associated with secondary albitic plagioclase, indicating coupled formation. The NaCl most likely formed through precipitation from an aqueous fluid prior to complete metamorphic dehydration on asteroid Itokawa. Our results therefore imply that asteroid Itokawa supported an active hydrothermal system and suggest that the once-hydrated S-type asteroids could have potentially delivered water to terrestrial planets.

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Fig. 1: HAADF image and associated EDS X-ray maps of FIB Section no. 3.
Fig. 2: Higher-magnification SE images of NaCl grains in FIB Section no. 3.
Fig. 3: TEM images and EDS X-ray maps of FIB Section no. 5 showing the presence of a vein that transects the section and associated NaCl grains.
Fig. 4: Comparison of SAED patterns acquired from plagioclase and the vein in FIB Section no. 5.

Data Availability

All data supporting this study are provided in Results section of this paper and the supplementary information accompanying this paper. Source data are provided with this paper.


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This research was supported by the NASA Laboratory Analysis of Returned Samples grant no. 80NSSC19K0509 awarded to T.J.Z. We acknowledge NASA grant no. NNX12AL47G and no. NNX15AJ22G, and NSF grant no. 1531243 and no. 0619599 for funding the instrumentation in the KMICF at the Lunar and Planetary Laboratory, UA. We thank R. Downs in the Department of Geosciences, UA for the loan of the terrestrial albite sample. We greatly appreciate members of the Planetary Materials Research Group at the Lunar and Planetary Laboratory for very helpful feedback and suggestions. S.C. would like to thank P.-M. Zanetta for helpful conversations on quantification of EDS spectra and L. Keller, J. Lewis and M. Zolotov for useful information and discussions. S.C. also appreciates Z. Zeszut, T. Ramprasad and Y.-J. Chang for their assistance with FIB and TEM operations.

Author information

Authors and Affiliations



S.C. prepared the FIB sections of the terrestrial albite sample, carried out part of the TEM analyses and wrote the paper. T.J.Z. prepared the FIB sections of Itokawa particle RA-QD02-0248 and conducted part of the TEM analyses. Both authors contributed to the data interpretation and discussions and revision of the paper.

Corresponding author

Correspondence to Shaofan Che.

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Nature Astronomy thanks Makoto Kimura and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Text, Figs. 1–15, Tables 1 and 2 and References.

Source data

Source Data Fig. 1

Unprocessed HAADF and EDS X-ray maps.

Source Data Fig. 2

Unprocessed TEM SE images.

Source Data Fig. 3

Unprocessed BF-TEM, HAADF and EDS X-ray maps.

Source Data Fig. 4

Unprocessed SAED patterns.

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Che, S., Zega, T.J. Hydrothermal fluid activity on asteroid Itokawa. Nat Astron 7, 1063–1069 (2023).

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