Reconstructing the aqueous environment of the Ryugu parent body through the speciation of multiple elements
Year: 2026
Type: article
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.
Source: Nature Communications
Authors: Takahiro Kawai, Keisuke Fukushi, Tomohiro Ohno, Hiroki Suga, Masayuki Uesugi, Ayu Takemoto, Akiko Yamaguchi, Takaaki Itai, Yuta Ijichi, Shohei Yamashita, Yasuhiro Niwa, Ryoichi Nakada, Mizuho Koike, Hideto Yoshida, Masaki Oura, Megumi Matsumoto, Tomohiro Usui, Yoko Kebukawa, Takazo Shibuya, Shogo Tachibana, Yasuhito Sekine, Tomoki Nakamura, Yoshio Takahashi
Institutions: The University of Tokyo, Kanazawa University, Kanazawa Institute of Technology, Japan Synchrotron Radiation Research Institute, Japan Atomic Energy Agency, Japan Agency for Marine-Earth Science and Technology, High Energy Accelerator Research Organization, Hiroshima University, SPring-8, Tohoku University, Japan Aerospace Exploration Agency, Tokyo Institute of Technology, Life Science Institute
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $6,990
Awards: バイオミネラリゼーションにおける有機・無機相互作用の分子レベルでの理解, レアアースのイオン吸着型鉱床の分子地球化学：その形成機構・探査・抽出法・モデル化, Astrobiology of C-type Asteroids: New Frontiers in Molecular Geochemistry, G394442828, 走査型透過X線顕微鏡と合成実験による隕石中の有機物の生成過程解明, Reconstruction of the water chemistry of the first water in the solar system: Systematic prediction of biomolecules in C-type asteroids, Origin and evolution of aqueous fluids in early solar system small bodies: a study on fluid inclusions in primitive solar system materials, G7074573581, G7767375815, 粘土鉱物中のFeの酸化状態が元素の挙動に及ぼす影響の理解, スメクタイト構造中の鉄による酸化還元反応が気候変動に与える影響の解明
OpenAlex ID: W7222510089