Nanoscale Spectroscopic Identification and Characterization of Minerals and Organic Matter in Ryugu Particles

Carbonaceous asteroids are leftover materials from the early solar system. They did not undergo planetary differentiation processes and thus still retained signatures and clues of the origin and evolution of the solar system. Thus, samples of carbonaceous asteroids provide significant potential for deciphering the origin of the solar system. The Hayabusa2 spacecraft returned the first samples of a carbonaceous asteroid (162173) Ryugu. In this work, we report the nanoscale mineralogy and organic matter content of two Ryugu particles, A0030 and C0034. These were analyzed by highly novel scattering-type scanning near-field optical microscopy (s-SNOM)-based nanoscale-Fourier transform infrared (nano-FTIR) spectroscopy with similar to 20 nm spatial resolution. The nano-FTIR measurements were supported by confocal micro-Raman imaging and spectroscopy (similar to 500 nm/pixel spatial sampling). Our investigations show that the two Ryugu particles (a) contain different silicate mineralogies, indicating heterogeneous and incomplete aqueous alteration and (b) are highly rich in organic matter, consisting a variety of molecular functional groups. The spatial distributions of chemical functional groups and their associations based on pseudo-heterodyne (PsHet) SNOM imaging show that the organic matter is distributed as either diffused or discrete grains. Micro-Raman spectra show that the Ryugu particles experienced minimal thermal metamorphism, although A0030 was slightly more heated than C0034. The identification of abundant nanoscale organic molecules within the Ryugu grains that could not be identified via micrometer-scale investigations emphasizes the importance of using nanoscale nondestructive methods for studying primitive solar system materials, such as Ryugu and OSIRIS-Rex particles and those that will be returned in the future (such as MMX samples). Asteroids are left over materials from the early formation of our solar system similar to 4.57 billion years ago. Carbonaceous asteroids contain minerals that are capable of synthesizing a variety of organic molecules. Indeed, carbonaceous asteroids contain abundant organic matter. For the first time, samples of a carbonaceous asteroid Ryugu were returned to Earth by JAXA in late 2020. The returned asteroid samples provided uncontaminated pristine organic compositions. Investigations of Ryugu samples can provide clues to understanding planet formation processes as well as the origin and evolution of the early solar system. We show the chemical composition of two Ryugu particles determined by highly novel multiscale spectroscopic and microscopic methods. Nanoscale infrared spectroscopy shows the presence of different phyllosilicate mineralogies, indicative of incomplete and heterogeneous aqueous alteration in the parent asteroid. Our results also show the presence of abundant and heterogeneous organic matter with different structural properties (diffuse vs. discrete) in the Ryugu particles, which are due to complex formation and evolution of these molecules. Nanoscale mineralogy and organic matter content of Ryugu asteroid particles have been determined The investigated Ryugu particles have been determined to be highly rich in organic matter, and present complex organic chemistry Ryugu particles show incomplete and heterogeneous aqueous alteration and experience minimal and varying thermal metamorphism