Presentation Information
[R5-11]Investigation of sodium salt minerals in Ryugu samples
*Toru MATSUMOTO1, Takaaki Noguchi2, Akira Miyake2 (1. Kyoto Univ. Hakubi, 2. Kyoto Univ. Sci.)
Keywords:
Ryugu
Recent studies of Ryugu samples have reported the presence of sodium carbonates, chlorides, and sulfates, indicating that alkaline, salt-rich water in its parent body [1]. The precipitation of sodium salt minerals was likely accompanied by dynamic changes in water content and chemical composition. These minerals were also found in samples from asteroid Bennu [2], and provide a unique opportunity to gain new insights into the chemical evolution of water-rich carbonaceous asteroids. The study of sodium salt minerals has only just begun, and further investigation is required.
Methods: The surface of Ryugu sample C0071 was investigated by SEM Several sections from these sodium-rich regions were then extracted using a FIB and subsequently examined using TEM.
Results: Ryugu grain C0071 is mainly composed of phyllosilicates (saponite and serpentine), iron- and nickel-bearing sulfides, and magnetite, indicating an aqueously altered lithology. Aggregates of sodium-rich natrite was identified on the surface of the phyllosilicates. Natrite also occurs as a vein filling the interface between the Na-Mg phosphate and the surrounding matrix. Thenardite was identified adjacent to the natrite, based on electron diffraction patterns. A calcite grain measuring about 1 µm in size is found in contact with the natrite grains.
Discussion: The sodium carbonates and sulfates may have formed by the evaporation or freezing of liquid water during the final stages of aqueous alteration. In the evaporation sequence of alkaline solution, calcite grain can form through incongruent dissolution of primary gaylussite [3], which is found in Bennu samples. Therefore, the calcite associated with natrite in the Ryugu sample could have formed during the later stages of aqueous alteration, whereas the majority of calcite in Ryugu samples formed in an early-stage product [4]. The similarity in sodium salt mineralogy between Ryugu and Bennu suggests that their brines may have evolved in comparable ways.
Reference: [1] Matsumoto, T., et al. (2024). Nature Astronomy, 8, 1536-1543. [2] McCoy, T. J., et al. (2025) Nature, 637(8048), 1072-1077. [3] Toner, J., D., et al. (2020) PNAS, 117. 2.,883-888. [4]Fujiya, W., et al. (2023) Nature Geoscience, 16.8, 675-682.
Methods: The surface of Ryugu sample C0071 was investigated by SEM Several sections from these sodium-rich regions were then extracted using a FIB and subsequently examined using TEM.
Results: Ryugu grain C0071 is mainly composed of phyllosilicates (saponite and serpentine), iron- and nickel-bearing sulfides, and magnetite, indicating an aqueously altered lithology. Aggregates of sodium-rich natrite was identified on the surface of the phyllosilicates. Natrite also occurs as a vein filling the interface between the Na-Mg phosphate and the surrounding matrix. Thenardite was identified adjacent to the natrite, based on electron diffraction patterns. A calcite grain measuring about 1 µm in size is found in contact with the natrite grains.
Discussion: The sodium carbonates and sulfates may have formed by the evaporation or freezing of liquid water during the final stages of aqueous alteration. In the evaporation sequence of alkaline solution, calcite grain can form through incongruent dissolution of primary gaylussite [3], which is found in Bennu samples. Therefore, the calcite associated with natrite in the Ryugu sample could have formed during the later stages of aqueous alteration, whereas the majority of calcite in Ryugu samples formed in an early-stage product [4]. The similarity in sodium salt mineralogy between Ryugu and Bennu suggests that their brines may have evolved in comparable ways.
Reference: [1] Matsumoto, T., et al. (2024). Nature Astronomy, 8, 1536-1543. [2] McCoy, T. J., et al. (2025) Nature, 637(8048), 1072-1077. [3] Toner, J., D., et al. (2020) PNAS, 117. 2.,883-888. [4]Fujiya, W., et al. (2023) Nature Geoscience, 16.8, 675-682.