A propensity for n‐ω‐amino acids in thermally altered Antarctic meteorites

Abstract

Abstract-Asteroids and their fragments have impacted the Earth for the last 4.5 Gyr. Carbonaceous meteorites are known to contain a wealth of indigenous organic molecules, including amino acids, which suggests that these meteorites could have been an important source of prebiotic organic material during the origins of life on Earth and possibly elsewhere. We report the detection of extraterrestrial amino acids in thermally altered type 3 CV and CO carbonaceous chondrites and ureilites recovered from Antarctica. The amino acid concentrations of the thirteen Antarctic meteorites ranged from 300 to 3200 parts-per-billion (ppb), generally much less abundant than in amino acid-rich CI, CM, and CR carbonaceous chondrites that experienced much lower temperature aqueous alteration on their parent bodies. In contrast to low-temperature aqueously altered meteorites that show complete structural diversity in amino acids formed predominantly by Streckercyanohydrin synthesis, the thermally altered meteorites studied here are dominated by small, straightchain, amine terminal (n-x-amino) amino acids that are not consistent with Strecker formation. The carbon isotopic ratios of two extraterrestrial n-x-amino acids measured in one of the CV chondrites (d 13C approximately )25&) are consistent with 13 C-depletions observed previously in hydrocarbons produced by Fischer-Tropsch type reactions. The predominance of n-x-amino acid isomers in thermally altered meteorites hints at cosmochemical mechanisms for the preferential formation and preservation of a small subset of the possible amino acids.

Amino acid compositions in heated carbonaceous chondrites and their compound-specific nitrogen isotopic ratios

“…If thermal metamorphism is followed by aqueous alteration, the heat-recycled molecules could subsequently develop into ammonia and precursor carbonyl molecules, which can produce α-amino acids through Strecker synthesis, resulting in an amino acid content similar to that of Murchison which is dominated by α-amino acids such as α-AIB (Cronin and Moore 1971;Peltzer et al 1984). Conversely, if amino acid synthesis is followed by another heating episode where FTT reactions are feasible, the final amino acid inventory would comprise chiefly straight-chain amino acids like β-alanine and γ-ABA, similar to the result reported for the thermally altered meteorites (Burton et al 2012a). Lastly, if the asteroidal body had experienced an extensive heating regime, the heat would only serve to decompose any preexisting molecules, which likely describes what might have happened on ALHA77003.…”

“…Amino acids can also be produced by Fischer-Tropsch type (FTT) reactions at 200°to 700°C in the presence of CO, H 2 , NH 3 , and catalysts (Yoshino et al 1971). Despite the evidences of thermal metamorphism exhibited by Y-980115, its amino acid content is dissimilar to the previously analyzed thermally altered CV and CO chondrites, which were dominated by straight-chain amino acids (Burton et al 2012a). Nevertheless, glycine and alanine can also be synthesized by FTT reactions (Pizzarello 2012;Yoshino et al 1971); thus, the dissimilarity between the amino acid contents of Y-980115 to CV/CO chondrites does not necessarily rule out FTT reactions as the possible amino acid formation pathway for this meteorite.…”

“…The isotopic compositions of Y-980115 and ALHA77003 were obtained using EA/IRMS in this study a Data from this study were the average of duplicate analyses (n = 2) b Data were previously reported by Kerridge (1985) and references therein here, we compare its low amino acid abundance to other CO3 chondrites. Likewise, CO3 chondrites generally present low amino acid concentrations as compared to other chondritic types, and the range of amino acid concentrations is present in large variability (total amino acid abundance 260-2400 ppb) (Burton et al 2012a;Chan et al 2012;Glavin et al 2010). Petrologic type 3 meteorites often represent the most pristine materials.…”

One-pot synthesis of amino acid precursors with insoluble organic matter in planetesimals with aqueous activity

“…For the thermally metamorphosed chondrites, there could be some contributions from n -ω-amino acids produced by FTT reactions in their parent bodies ( 24 ). …”

Planning Considerations Related to the Organic Contamination of Martian Samples and Implications for the Mars 2020 Rover

“…3-Amino-2,2-dimethylpropanoic acid (Callahan, unpublished data), and Graves Nunataks Antarctic ice (Burton et al, 2012). All values are reported in parts per billion (ppb) on a bulk sample basis except where noted.…”