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Meteoritic evidence for a Ceres-sized water-rich carbonaceous chondrite parent asteroid

An Addendum to this article was published on 25 October 2021


Carbonaceous chondrite meteorites record the earliest stages of Solar System geological activities and provide insight into their parent bodies’ histories. Some carbonaceous chondrites are volumetrically dominated by hydrated minerals, providing evidence for low-temperature, low-pressure aqueous alteration1. Others are dominated by anhydrous minerals and textures that indicate high-temperature metamorphism in the absence of aqueous fluids1. Evidence of hydrous metamorphism at intermediate pressures and temperatures in carbonaceous chondrite parent bodies has been virtually absent. Here we show that an ungrouped, aqueously altered carbonaceous chondrite fragment (numbered 202) from the Almahata Sitta (AhS) meteorite contains an assemblage of minerals, including amphibole, that reflect fluid-assisted metamorphism at intermediate temperatures and pressures on the parent asteroid. Amphiboles are rare in carbonaceous chondrites, having only been identified previously as a trace component in Allende (CV3oxA) chondrules2. Formation of these minerals would require prolonged metamorphism in a large (about 640–1,800 kilometres in diameter) asteroid that is as yet unknown. Because Allende and AhS 202 represent different asteroidal parent bodies, intermediate conditions may have been more widespread in the early Solar System than is recognized from known carbonaceous chondrite meteorites, which are likely to represent a biased sampling.

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Fig. 1: Backscattered electron (atomic number contrast) image of AhS 202.
Fig. 2: Infrared spectra from AhS 202, terrestrial amphiboles and model fit.
Fig. 3: X-ray elemental and backscattered electron images of minerals and textures in AhS 202.

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V.E.H., C.A.G. and M.E.Z. are supported by grant 80NSSC19K0507 from NASA’s Emerging Worlds programme. M.E.Z. was also supported by the Hayabusa2 Participating Scientist Program (NASA). A. Fioretti initially recognized and selected AhS 202 for analysis, made the mount and collected early scanning electron microscopy observations. We thank J. Filiberto (LPI/USRA) for contributing to scientific discussions. The Lunar and Planetary Institute (LPI) is operated by Universities Space Research Association (USRA) under a cooperative agreement with the Science Mission Directorate of NASA. This is LPI Contribution no. 2546.

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Authors and Affiliations



V.E.H. conducted and analysed the spectral measurements, contributed to the scientific interpretation, and coordinated and wrote the manuscript. C.A.G. conducted and analysed the scanning electron microscopy and EMPA measurements, performed the parent-body size modelling, and contributed to the scientific interpretation of all data. A.H.T. contributed to the metamorphic mineral assemblage modelling and textural interpretations. H.C.C. contributed to the scientific interpretation of the observed EPMA, textural and spectral results. M.E.Z. conducted EMPA and TEM measurements and contributed to the scientific interpretation of those data. M.H.S. provided the sample of AhS 202 from the University of Khartoum collection.

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Correspondence to V. E. Hamilton.

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Peer review information Nature Astronomy thanks Jemma Davidson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Hamilton, V.E., Goodrich, C.A., Treiman, A.H. et al. Meteoritic evidence for a Ceres-sized water-rich carbonaceous chondrite parent asteroid. Nat Astron 5, 350–355 (2021).

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