Electron microscopy observations of the diversity of Ryugu organic matter and its relationship to minerals at the micro- to nano-scale

Abstract

Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range of morphologies, elemental compositions, and carbon functional chemistries consistent with those of carbonaceous chondrites that have experienced low-temperature aqueous alteration. Both nanoglobules and diffuse organic matter are abundant. Non-globular organic particles are also present, and including some that contain nanodiamond clusters. Diffuse organic matter is finely distributed in and around phyllosilicates, forms coatings on other minerals, and is also preserved in vesicles in secondary minerals such as carbonate and pyrrhotite. The average elemental compositions determined by energy-dispersive spectroscopy of extracted, demineralized insoluble organic matter samples A0107 and C0106 are C₁₀₀N₃O9S1 and C₁₀₀N₃O₇S₁, respectively, with the difference in O/C slightly outside the difference in the standard error of the mean. The functional chemistry of the nanoglobules varies from mostly aromatic C=C to mixtures of aromatic C=C, ketone C=O, aliphatic (CHₙ), and carboxyl (COOH) groups. Diffuse organic matter associated with phyllosilicates has variable aromatic C, ketone and carboxyl groups, and some localized aliphatics, but is dominated by molecular carbonate (CO₃) absorption, comparable to prior observations of clay-bound organic matter in CI meteorites.