The Amino Acid Distribution in Laboratory Analogs of Extraterrestrial Organic Matter: A Comparison to CM Chondrites

Abstract

Laboratory experiments that simulate the photo-and thermo-chemistry of extraterrestrial ices always lead to the formation of semi-refractory organic residues. These residues can be considered as laboratory analogs for the primitive organic matter incorporated into comets and asteroids. Many specific organic molecules have been detected in them. Here we focus on amino acids because of their possible relevance to further prebiotic chemistry on Earth as well as in other solar system bodies. We compare the amino acid content and distribution measured in organic residues produced in our photochemical experiments to those observed in various CM chondrites presenting an increasing degree of aqueous alteration, a process that is thought to impact amino acid chemistry. We find that the amino acid profile of our residues shows similarities with that of the least aqueously altered CM chondrites. In particular, the β-alanine to glycine ratio is comparable to the one measured in the Paris meteorite, a minimally altered CM chondrite, and matches the trend followed by other CM chondrites with different degrees of aqueous alteration. Additionally, the relative abundances of α-, β-, and γ-amino acids in one of our residues are similar to those of the least altered CM chondrites. These results support the idea of a general formation process for amino acids from photo-and thermo-processing of icy grains as an important source for the inventory of amino acids in the early solar system.

Extraterrestrial organic compounds and cyanide in the CM2 carbonaceous chondrites Aguas Zarcas and Murchison

“…Thus, the lower amounts of acid-releasable CN À measured in this study can be explained by a combination of water extraction before mineral distillation and potential sample heterogeneity. The larger amount of acid-releasable CN À in Aguas Zarcas UA 2741-1 than in Murchison may suggest that Aguas Zarcas UA 2741-1 experienced slightly lower levels of aqueous alteration than Murchison, a hypothesis that is consistent with the lower ratio of the amino acid balanine to glycine in Aguas Zarcas (Modica et al 2018;Glavin et al 2020) and with petrographic observations and in situ geochemical analyses of Aguas Zarcas (Martin and Lee 2020). However, more analyses are needed to fully understand the origins, forms, and abundances of CN À in carbonaceous chondrites as this and previous analyses suggest that CN À was more readily available in the meteorites and thus the early Earth, than previously thought.…”

Prebiotic Chemistry of Pluto

“…Because some nucleobases are degraded in an aqueous environment, the final distribution of the individual molecular species ultimately depends on the balance between synthesis and degradation. Recent laboratory work (Modica et al 2018) supports the view that an important source of amino acids in the early Solar System arises from photo-and thermo-processing of icy grains prior to accretion in planetary bodies.…”

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

“…; Modica et al. ). TL4 and TL10a are also unusual as their amino acid compositions are nearly identical, despite some clear differences in their organic contents and bulk properties.…”

“…The amino acid compositions observed in the present study and previously for Tagish Lake samples exhibit some inconsistencies compared to general trends observed among carbonaceous chondrites. For example, the high relative abundances of c-ABA and b-alanine observed in what are interpreted as moderately altered samples (TL1 and TL5b) is unusual; generally, higher relative abundances of band c-amino acids are considered indicators of higher levels of aqueous alteration Glavin et al 2011;Elsila et al 2016;Modica et al 2018). TL4 and TL10a are also unusual as their amino acid compositions are nearly identical, despite some clear differences in their organic contents and bulk properties.…”