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

Vol. 684
10. Planets and planetary systems

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

by Jérémie Mathurin, Laure Bejach, Emmanuel Dartois, et al. 2024, A&A, 684, A198 alt

Vibrational spectroscopy is a powerful tool to investigate the chemical structure of organic matter and minerals in meteorites, micrometeorites, and return samples from space missions. "Classic" infrared microspectrocopy (µ-FTIR) is, however, diffraction limited to spatial resolutions of a few microns. Infrared photothermal nanospectrocopy (AFM-IR), which combines the chemical analysis power of infrared spectroscopy and the high spatial resolution of scanning probe microscopy, yields a hundred times better lateral spatial resolution (i.e., approximately a few 10 nm) than µ-FTIR does. This novel technique has already been successfully applied to the organic matter of some meteorites and micrometeorites. For this work, Mathurin et al. performed AFM-IR nanospectroscopy of organic material in samples of the asteroid Ryugu, which returned to Earth by the Hayabusa2 mission in December 2020. This material includes whole-rock particles and insoluble organic matter (IOM) residues extracted from the samples. The authors identified that organic matter in the whole-rock samples is present in two forms, a diffuse phase intermixed with the phyllosilicate matrix and individual organic nanoparticles. The latter ones were identified as nanoglobule-like inclusions, resembling nanoglobules in primitive meteorites. The high lateral resolution allowed infrared spectra of the organic nanoparticles to be recorded for the first time, revealing enhanced carbonyl (C=O) and CH contributions with respect to the diffuse organic component. The results are consistent with scenarios in which nanoglobules are formed from UV or ion irradiation of ices in the outer regions of the protoplanetary disk or in the protosolar cloud.