Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements

The parent body of the C-type asteroid Ryugu experienced aqueous alteration. The past aqueous environments have been reconstructed using mineralogies and geochemical modeling, often assuming Na-Cl-rich fluid compositions. Here, we reconstruct Ryugu’s aqueous environment using chemical equilibrium modeling constrained by Electron Probe Microanalyzer (EPMA) and X-ray absorption near-edge structure spectroscopy. Our results suggest that Ryugu water possessed lower salinity than previously estimated and was highly reducing (Eh: −0.5 to −0.8 V) and strongly alkaline (pH: 10.3 to 11.5) conditions conducive to prebiotic organic reactions. The inferred high hydrogen fugacity, lack of NaCl, and low salinity recorded in Ryugu sample suggest that aqueous alteration occurred beneath a surface ice layer, with subsequent ice sublimation driving water loss. These findings refine our understanding of C-type asteroids evolution and the quantity and nature of water delivered to the early Earth. Analysis of the elemental species composition of returned samples from the C-type asteroid Ryugu indicates that Ryugu’s aqueous environment was highly reducing and strongly alkaline, conditions conducive to prebiotic organic reactions.

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Publication Details

Journal
Nature Communications
Published
2026-10-16
DOI
https://doi.org/10.1038/s41467-026-78348-5
Primary Topic
Astro and Planetary Science
Type
article
Field-Weighted Citation Impact
0.00

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article

Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements

Masaki Oura, Megumi Matsumoto, Takaaki Itai, Yoshio Takahashi et al.
Nature Communications
Astro and Planetary Science
article

Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements

Masaki Oura, Megumi Matsumoto, Takaaki Itai, Yoshio Takahashi, Ryoichi Nakada, Yoko Kebukawa, Shohei Yamashita, Shogo Tachibana, Takazo Shibuya, Mizuho Koike, Yasuhiro Niwa, Tomoki Nakamura, T. Kawai, Tomohiro Usui, Masayuki Uesugi, Yuta Ijichi, A. Yamaguchi, Hiroki Suga, Yasuhito Sekine, Keisuke Fukushi, Hideto Yoshida, Ayu TAKEMOTO, Ohno Tomohiro
article en

Abstract

The parent body of the C-type asteroid Ryugu experienced aqueous alteration. The past aqueous environments have been reconstructed using mineralogies and geochemical modeling, often assuming Na-Cl-rich fluid compositions. Here, we reconstruct Ryugu’s aqueous environment using chemical equilibrium modeling constrained by Electron Probe Microanalyzer (EPMA) and X-ray absorption near-edge structure spectroscopy. Our results suggest that Ryugu water possessed lower salinity than previously estimated and was highly reducing (Eh: −0.5 to −0.8 V) and strongly alkaline (pH: 10.3 to 11.5) conditions conducive to prebiotic organic reactions. The inferred high hydrogen fugacity, lack of NaCl, and low salinity recorded in Ryugu sample suggest that aqueous alteration occurred beneath a surface ice layer, with subsequent ice sublimation driving water loss. These findings refine our understanding of C-type asteroids evolution and the quantity and nature of water delivered to the early Earth. Analysis of the elemental species composition of returned samples from the C-type asteroid Ryugu indicates that Ryugu’s aqueous environment was highly reducing and strongly alkaline, conditions conducive to prebiotic organic reactions.

Nature CommunicationsVol. 17(1)
Kanazawa University (JP), Hiroshima University (JP), Tokyo Institute of Technology (JP), Japan Atomic Energy Agency (JP), Kanazawa Institute of Technology (JP), Japan Agency for Marine-Earth Science and Technology (JP), High Energy Accelerator Research Organization (JP), Tohoku University (JP), Japan Aerospace Exploration Agency (JP), SPring-8 (JP), Japan Synchrotron Radiation Research Institute (JP), Life Science Institute (JP), The University of Tokyo (JP)
Japan Society for the Promotion of Science, Japan Aerospace Exploration Agency
Openalex Percentile: Top 14%
Astro and Planetary Science
DOIOpen Access PDFOpenAlex
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