Challenges and Opportunities in Using Amino Acids to Decode Carbonaceous Chondrite and Asteroid Parent Body Processes.

Abstract

Carbonaceous chondrite (CC) meteorites are fragments of planetesimals that hold clues about the early solar system's organic matter. Amino acids are key to life on Earth; thus their study from extraterrestrial samples may help identify signs of prebiotic chemistry and life on other planets and may reveal how life as we know it began. This study analyzed amino acid concentrations and distributions in 42 CC samples, including returned samples from asteroids Ryugu and Bennu, to investigate the relationship between amino acid composition and parent body processes. We performed a statistical analysis of the amino acid molecular distributions and abundances in the context of meteoritic hydrogen, carbon, nitrogen, and carbonate total contents to explore the links between these organic species and thermal and aqueous processing experienced in the parent bodies. We also evaluated whether meteoritic amino acid ratios can be used as anti-biosignatures, and we re-evaluated the links between l-isovaline enantiomeric excesses and parent body aqueous alteration. While some trends were observed, correlations between amino acid distributions and alteration proxies (H, C, N, carbonates, enantiomeric excess) were generally weak, which indicates the need for larger sample sets. Thermal metamorphism correlated with lower amino acid and elemental [hydrogen (H), carbon (C), and nitrogen (N)] abundances, consistent with diverse parent bodies or localized processing. Ryugu samples exhibited significant amino acid variations despite similar bulk elemental compositions due to parent body heterogeneity. No strong statistical correlations were found between amino acid concentrations and H, C, or N content, which diminishes the reliability of predictions of amino acid abundances based solely on observed elemental abundances. While Ryugu and Bennu may share a common, Ceres-like parent body, observed differences in chemical composition suggest diverse evolutionary pathways. Finally, principal component analysis of amino acid and elemental data revealed distinct groupings that place Ryugu samples in a potentially unique subgroup and Bennu within the C2-ung chondrite group. These findings underscore the need for further study of such materials, especially given our discovery of their distinct nature, and emphasizes the insights gleaned from the ability to analyze returned asteroid samples.