Organic molecular signatures of aqueous alteration at Ryugu and the perspectives

<p>Pristine samples from the asteroid (162173) Ryugu by the Hayabusa2 spacecraft provided a valuable opportunity to reveal the organic astrochemistry in the Solar System [1]. Hayabusa2 soluble organic matter (hereafter, SOM) team [2,3] evaluated aggregate fine grain samples from the first and second touchdown sites (hereafter, TD1 and TD2) for the surface (A0106) and possibly subsurface (C0107) environments of Ryugu. The SOM team determined the elemental profiles on carbon (C), nitrogen (N), hydrogen (H), pyrolyzable oxygen (O), sulfur (S) elements and their isotopic compositions [2,3], amino acids and their molecular chirality [4], pyrimidine nucleobase and N-heterocycles [5], primordial salts and sulfur-bearing labile molecules between the organic and inorganic interface [6], polycyclic aromatic hydrocarbons (PAHs) [7], sub-mm scale spatial imaging for organic homogeneity and heterogeneity in the mineral assemblage [8], and comprehensive organic molecular profiles on cold hydrothermalism on the asteroid [9]. The systematics for elemental and organic chemical surveys for CNHOS and hydrophilic molecular groups were summarized to formulate the TD1 and TD2 profiles; e.g., total CNHOS in the initial bulk of A0106 and C0107 are ~21.3 wt% and ~23.7 wt%, respectively [2,3]. Within these overviews of surface and potential subsurface sample analysis, we evaluated the average chemical composition and diversity of hydrophilic molecules to determine whether there is potential organic heterogeneity or homogeneity in Ryugu regolith. We newly identified the series of hydrophilic organic molecules as a crucial record of indigenous water-organic interactions [3,6] among these molecular surveys. Here, we discuss the primordial aqueous alteration signatures in the asteroid Ryugu based on unique hydrophilic molecular isomerism.References: [1] Tachibana et al. (2022) Science; Yada et al. (2022) Nature Astron. [2] Naraoka et al. (2023) Science. [3] Takano et al. (2024) Nature Commun. [4] Parker et al. (2023) Geochim. Cosmochim. Acta. [5] Oba et al. (2023) Nature Commun. [6] Yoshimura et al. (2023) Nature Commun. [7] Aponte et al. (2023) Earth Planet Space.; Zeichner et al. (2023) Science. [8] Hashiguchi et al. (2023) Earth Planet Space. [9] Schmitt-Kopplin et al. (2023) Nature Commun. [10] Oba et al. (2023) Nature Commun.; Lauretta et al. (2024) Meteorit. & Planet. Sci.</p>