AFM-IR nanospectroscopy of nanoglobule-like particles in Ryugu samples returned by the Hayabusa2 mission

¹ Institut Chimie Physique, UMR8000, Univ. Paris-Saclay, CNRS, 91405 Orsay, France
e-mail: jeremie.mathurin@universite-paris-saclay.fr
² Laboratoire de Physique des deux infinis Irène Joliot Curie, UMR 9012, Univ. Paris-Saclay, CNRS, 91405 Orsay, France
³ Institut des Sciences Moléculaires d’Orsay, UMR8214, CNRS, Univ. Paris-Saclay, 91405 Orsay, France
⁴ Institut de Minéralogie, Physique des Matériaux et de Cosmochimie, Museum National d’Histoire Naturelle, CNRS, Sorbonne Université, 75231 Paris, France
⁵ Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan
⁶ Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁷ Institut de Planétologie et d’Astrophysique, Université Grenoble Alpes, 38000 Grenoble, France
⁸ Synchrotron SOLEIL, CNRS, CEA, Paris-Saclay, 91190, Saint-Aubin, France
⁹ Earth and Planets Laboratory, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, USA
¹⁰ Materials Science and Technology Division, US Naval Research Laboratory, Washington, DC 20375, USA
¹¹ Graduate School of Environmental Studies, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
¹² Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720-8229, USA
¹³ The Graduate University for Advanced Studies, SOKENDAI, Hayama, Kanagawa 240-0193, Japan
¹⁴ Department of Earth Sciences, Waseda University, Shinjuku-ku, Tokyo 169-8050, Japan
¹⁵ Centro de Química Estrutural, Institute of Molecular Sciences and Department of Chemical Engineering, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
¹⁶ Department of Earth Sciences, Tohoku University, Sendai 980-8578, Japan
¹⁷ École normale supérieure de Lyon, Université de Lyon, 69342 Lyon, France
¹⁸ Institute for Molecular Science, UVSOR Synchrotron Facility, Myodaiji, Okazaki 444-8585, Japan
¹⁹ Department of Earth and Planetary Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁰ NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
²¹ Materials Science and Technology Division, US Naval Research Laboratory, Washington, DC 20375, USA
²² Spectroscopy Division, Japan Synchrotron Radiation Research Institute JASRI), Sayo-gun, Hyogo 679-5198, Japan
²³ Institute of Materials Structure Science, High Energy Accelerator Research Organization, KEK, Tsukuba, Ibaraki 305-0801, Japan
²⁴ Research and Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo-gun, Hyogo 679-5198, Japan
²⁵ Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan
²⁶ Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 819-0395, Japan
²⁷ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
²⁸ Department of Natural History Sciences, Hokkaido University, Sapporo 060-0810, Japan
²⁹ Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo 001-0021, Japan
³⁰ Kanagawa Institute of Technology, Atsugi 243-0292, Japan
³¹ Department of Earth and Planetary Sciences, Nagoya University, Nagoya 464-8601, Japan

Received: 11 July 2023
Accepted: 18 January 2024

Abstract

Context. The JAXA Hayabusa2 mission returned well-preserved samples collected from the carbonaceous asteroid Ryugu, providing unique non-terrestrially weathered samples from a known parent body.

Aims. This work aims to provide a better understanding of the formation and evolution of primitive asteroidal matter by studying the fine scale association of organic matter and minerals in Ryugu samples. We characterized the samples by IR nanospectroscopy using infrared photothermal nanospectroscopy (AFM-IR) technique. This technique overcomes the diffraction limit (of several microns) of conventional infrared microspectroscopy (µ-FTIR). The samples were mapped in the mid-IR range at a lateral spatial resolution about a hundred times better than with µ-FTIR. This provided us with unique in situ access to the distribution of the different infrared signatures of organic components at the sub-micron scale present in the Ryugu whole-rock samples as well as to the characterization of the compositional variability of Ryugu in the insoluble organic matter (IOM) chemically extracted from the Ryugu samples.

Methods. The AFM-IR maps of whole-rock particles and IOM residues from Ryugu samples were recorded with a lateral resolution of tens of nanometers. Spectra were recorded in the 1900–900 cm⁻¹ spectral range by AFM-IR (Icon-IR) for all samples, and additional spectra were recorded from 2700 to 4000 cm⁻¹ for one IOM sample by an optical photothermal IR (O-PTIR) technique using a mIRage® IR microscope.

Results. Organic matter is present in two forms in the whole-rock samples: as a diffuse phase intermixed with the phyllosilicate matrix and as individual organic nanoparticles. We identify the Ryugu organic nanoparticles as nanoglobule-like inclusions texturally resembling nanoglobules present in primitive meteorites. Using AFM-IR, we record for the first time the infrared spectra of Ryugu organic nanoparticles that clearly show enhanced carbonyl (C=O) and CH contributions with respect to the diffuse organic matter in Ryugu whole-rock and IOM residue.