The amino acid and polycyclic aromatic hydrocarbon compositions of the promptly recovered CM2 Winchcombe carbonaceous chondrite

Chan, Queenie H. S.; Watson, Jonathan S.; Sephton, Mark A.; O'Brien, Áine C. and Hallis, Lydia J. (2023). The amino acid and polycyclic aromatic hydrocarbon compositions of the promptly recovered CM2 Winchcombe carbonaceous chondrite. Meteoritics & Planetary Science (Early Access).

DOI: https://doi.org/10.1111/maps.13936

Abstract

The rapid recovery of the Winchcombe meteorite offers a valuable opportunity to study the soluble organic matter (SOM) profile in pristine carbonaceous astromaterials. Our interests in the biologically relevant molecules, amino acids—monomers of protein, and the most prevalent meteoritic organics—polycyclic aromatic hydrocarbons (PAHs) are addressed by analyzing the solvent extracts of a Winchcombe meteorite stone using gas chromatography mass spectrometry. The Winchcombe sample contains an amino acid abundance of ~1132 parts‐per‐billion that is about 10 times lower than other CM2 meteorites. The detection of terrestrially rare amino acids, including α‐aminoisobutyric acid (AIB); isovaline; β‐alanine; α‐, β‐, and γ‐amino‐n‐butyric acids; and 5‐aminopentanoic acid, and the racemic enantiomeric ratios (D/L = 1) observed for alanine and isovaline indicate that these amino acids are indigenous to the meteorite and not terrestrial contaminants. The presence of predominantly α‐AIB and isovaline is consistent with their formation via the Strecker‐cyanohydrin synthetic pathway. The L‐enantiomeric excesses in isovaline previously observed for aqueously altered meteorites were viewed as an indicator of parent body aqueous processing; thus, the racemic ratio of isovaline observed for Winchcombe, alongside the overall high free:total amino acid ratio, and the low amino acid concentration suggest that the analyzed stone is derived from a lithology that has experienced brief episode(s) of aqueous alteration. Winchcombe also contains 2‐ to 6‐ring alkylated and nonalkylated PAHs. The low total PAHs abundance (6177 ppb) and high nonalkylated:alkylated ratio are distinct from that observed for heavily aqueously altered CMs. The weak petrographic properties of Winchcombe, as well as the discrepancies observed for the Winchcombe SOM content—a low total amino acid abundance comparable to heavily altered CMs, and yet the high free:total amino acid and nonalkylated:alkylated PAH ratios are on par with the less altered CMs—suggest that Winchcombe could represent a class of weak, poorly lithified meteorite not been previously studied.

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