Carbonaceous chondrites are meteoritic fragments of asteroids that avoided the geological reprocessing of larger planets and allow laboratory probing of early solar-nebula materials. Among these, Renazzo-type (CR) chondrites found in Antarctica appear remarkably pristine and are distinguished by abundant organic materials and water-soluble molecules such as amino acids and ammonia. We present a comprehensive analysis of the organic composition of selected CR meteorites of different petrographic classification and compare compounds' abundance and distribution as they may relate to asteroidal aqueous processing and concomitant evolution of the mineral phases. We found that several CR compounds such as amino acids and sugar alcohols are fully represented in stones with no or minimal water exposure indicating a formation that, if solar, preceded parent body processes. The most pristine CRs also revealed natal enantiomeric excesses (ee) of up to 60%, much larger than ever recorded. However, aqueous alteration appears to affect CR soluble organic composition and abundances, in particular some diastereomeric amino acids may gauge its extent by the consequent racemization of their ee.primitive asteroids | abiotic molecular evolution | solar ices | clays C R meteorites are characterized by several petrologic, geochemical, and isotopic features, such as containing large chondrules, high Fe-Ni metal abundances, and distinct wholerock O-isotopic distributions (1). However, only recent comprehensive analyses of the soluble and insoluble organic materials in two pristine* CR2 † meteorites, GRA 95229 (GRA1) and LAP 02342 (LAP) (2, 3) revealed what is possibly their most distinguishing characteristic vis-à-vis other carbonaceous chondrites (CC) types (i.e., soluble organic suites that are overall unique for having a preponderance of water-over solvent-soluble compounds). Ammonia is the most abundant single molecule detected in CR2 water extracts, and amino acids are their largest component, unlike, for example, in the Murchison meteorite where hydrocarbons are the dominant molecular species.Amino acids have been the most captivating findings in CC meteorites since the fall of Murchison (4) because several of the compounds have exact molecular correspondence with biomolecules and possible pre-biotic significance. In intervening studies, however, the detection of a diverse and apparently stochastic suite of compounds in many meteorites made it difficult to propose how this random mix could have found effective chemical pathways toward the origin of life (5). CR2s have significantly changed that perspective with their main compositional abundances of water-soluble and N-containing molecular species.CC materials relied on a long cosmic history for their formation, which spanned solar as well as presolar environments. In particular, the high D and 13 C isotopic enrichments of some CC organic compounds have revealed their lineage from cold cosmic regimes (6). Among CRs, GRA1 amino acids display δD values up to þ7;200‰ (2), the larges...

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To test the potential of using amino acid abundances as a biosignature at icy ocean worlds, we investigate whether primordial amino acids (accreted or formed by early aqueous processes) could persist until the present time. By examining the decomposition kinetics of amino acids in aqueous solution based on existing laboratory rate data, we find that all fourteen proteinogenic amino acids considered in this study decompose to a very large extent (>99.9%) over relatively short lengths of time in hydrothermally active oceans. Therefore, as a rule of thumb, we suggest that if amino acids are detected at Enceladus, Europa, or other hydrothermally active ocean worlds above a concentration of 1 nM, they should have been formed recently and not be relicts of early processes. In particular, the detection of aspartic acid (Asp) and threonine (Thr) would strongly suggest active production within the ocean, as these amino acids cannot persist beyond 1 billion years even at the freezing point temperature of 273K. Identifying amino acids from the oceans of icy worlds can provide key insight into their history of organic chemistry.

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