Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements
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.
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BibTeX
@article{kawai2026reconstructing,
title = {{Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements}},
author = {Takahiro Kawai and Keisuke Fukushi and Tomohiro Ohno and Hiroki Suga and Masayuki Uesugi and Ayu Takemoto and Akiko Yamaguchi and Takaaki Itai and Yuta Ijichi and Shohei Yamashita and Yasuhiro Niwa and Ryoichi Nakada and Mizuho Koike and Hideto Yoshida and Masaki Oura and Megumi Matsumoto and Tomohiro Usui and Yoko Kebukawa and Takazo Shibuya and Shogo Tachibana and Yasuhito Sekine and Tomoki Nakamura and Yoshio Takahashi},
journal = {Nature Communications},
year = {2026},
month = oct,
doi = {10.1038/s41467-026-78348-5},
url = {https://www.nature.com/articles/s41467-026-78348-5},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements
AU - Takahiro Kawai
AU - Keisuke Fukushi
AU - Tomohiro Ohno
AU - Hiroki Suga
AU - Masayuki Uesugi
AU - Ayu Takemoto
AU - Akiko Yamaguchi
AU - Takaaki Itai
AU - Yuta Ijichi
AU - Shohei Yamashita
AU - Yasuhiro Niwa
AU - Ryoichi Nakada
AU - Mizuho Koike
AU - Hideto Yoshida
AU - Masaki Oura
AU - Megumi Matsumoto
AU - Tomohiro Usui
AU - Yoko Kebukawa
AU - Takazo Shibuya
AU - Shogo Tachibana
AU - Yasuhito Sekine
AU - Tomoki Nakamura
AU - Yoshio Takahashi
PY - 2026
DA - 2026/10/16
JO - Nature Communications
DO - 10.1038/s41467-026-78348-5
UR - https://www.nature.com/articles/s41467-026-78348-5
AB - 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.
SN - 2041-1723
ER -