Meteoritic Amino Acids: Diversity in Compositions Reflects Parent Body Histories

Abstract

The analysis of amino acids in meteorites dates back over 50 years; however, it is only in recent years that research has expanded beyond investigations of a narrow set of meteorite groups (exemplified by the Murchison meteorite) into meteorites of other types and classes. These new studies have shown a wide diversity in the abundance and distribution of amino acids across carbonaceous chondrite groups, highlighting the role of parent body processes and composition in the creation, preservation, or alteration of amino acids. Although most chiral amino acids are racemic in meteorites, the enantiomeric distribution of some amino acids, particularly of the nonprotein amino acid isovaline, has also been shown to vary both within certain meteorites and across carbonaceous meteorite groups. Large l-enantiomeric excesses of some extraterrestrial protein amino acids (up to ∼60%) have also been observed in rare cases and point to nonbiological enantiomeric enrichment processes prior to the emergence of life. In this Outlook, we review these recent meteoritic analyses, focusing on variations in abundance, structural distributions, and enantiomeric distributions of amino acids and discussing possible explanations for these observations and the potential for future work.

Distribution of aliphatic amines in CO, CV, and CK carbonaceous chondrites and relation to mineralogy and processing history

“…; Elsila et al. ). Nevertheless, further evaluation of the total amine content (and that of other soluble meteoritic organics) in a larger set of samples belonging to these carbonaceous chondrite groups is needed to establish firmer correlations between meteorite types and amine abundances.…”

New insights into the heterogeneity of the Tagish Lake meteorite: Soluble organic compositions of variously altered specimens

“…The collective data suggest that Strecker synthesis was not the dominant reaction involved in amino acid production in TL1, but rather a process such as Michael addition or decarboxylation/deamination of dicarboxylic or diamino acids, which would result in relatively higher abundances of β‐ and γ‐amino acids, respectively (Elsila et al. ). The previously analyzed TL11h and TL5b samples are similarly enriched in β‐ and γ‐amino acids, and also contain relatively more α isomers, suggesting that they have recorded some additional input from Strecker synthesis type reactions.…”

The CM carbonaceous chondrite regolith Diepenveen

“…The ratio of five‐carbon amino acids based on amine position (α‐, β‐, γ‐, and δ‐) has been shown to correlate with mineralogy and parent body alteration (e.g., Elsila et al. ). In Diepenveen, the n ‐ω δ−aminovaleric acid dominates with much lower, but detectable, abundances of α‐, β‐, and γ‐ C5 amino acids.…”