Nature's Starships II: Simulating the Synthesis of Amino Acids in Meteorite Parent Bodies

Alyssa K. Cobb, Ralph E. Pudritz, Ben K. D. Pearce

Published 2015-06-22Version 1

Carbonaceous chondrite meteorites are known for having high water and organic material contents, including amino acids. Here we address the origin of amino acids in the warm interiors of their parent bodies (planetesimals) within a few million years of their formation, and connect this with the astrochemistry of their natal protostellar disks. We compute both the total amino acid abundance pattern as well as the relative frequencies of amino acids within the CM2 (e.g. Murchison) and CR2 chondrite subclasses based on Strecker reactions within these bodies. We match the relative frequencies to well within an order of magnitude among both CM2 and CR2 meteorites for parent body temperatures $<$ 200$^{\circ}$C. These temperatures agree with 3D models of young planetesimal interiors. We find theoretical abundances of approximately 7x10$^5$ parts-per-billion (ppb), which is in agreement with the average observed abundance in CR2 meteorites of 4$\pm$7x10$^5$, but an order of magnitude higher than the average observed abundance in CM2 meteorites of 2$\pm$2x10$^4$. We find that the production of hydroxy acids could be favoured over the production of amino acids within certain meteorite parent bodies (e.g. CI1, CM2) but not others (e.g. CR2). This could be due to the relatively lower NH$_3$ abundances within CI1 and CM2 meteorite parent bodies, which leads to less amino acid synthesis. We also find that the water content in planetesimals is likely to be the main cause of variance between carbonaceous chondrites of the same subclass. We propose that amino acid abundances are primarily dependent on the ammonia and water content of planetesimals that are formed in chemically distinct regions within their natal protostellar disks.