Organic Matter in Meteorites: Molecular and Isotopic Analyses of the Murchison Meteorite

Abstract

Carbonaceous chondrites comprise a unique subset of meteorites. Two classes of carbonaceous chondrites, the so-called CI1 and CM2 chondrites, are particularly interesting, in part because of their relatively high carbon content and the fact that most of this carbon is present as organic matter. This material is largely macromolecular but also contains a complex mixture of organic compounds that include carboxylic acids, dicarboxylic acids, amino acids, hydroxy acids, sulfonic acids, phosphonic acids, amines, amides, nitrogen heterocycles including purines and a pyrimidine, alcohols, carbonyl compounds, and aliphatic, aromatic, and polar hydrocarbons. The organic-rich CI1 and CM2 chondrites also contain an extensive clay mineralogy and other minerals that are believed to be indicative of an early episode of hydrous activity in the meteorite parent body. Recent stable isotope measurements have shown the organic matter in general, to be substantially enriched in deuterium and the discrete organic compounds to be enriched in 15N and somewhat enriched in 13C relative to terrestrial matter. These findings suggest that the organic matter is comprised of, or is closely related to, interstellar organic compounds. The organic chemistry of these meteorites is consistent with a formation scheme in which (1) a parent body was formed from volatile-rich icy planetesimals containing interstellar organic matter, (2) warming of the parent body led to an extensive aqueous phase in which the interstellar organics underwent various reactions, and (3) residual volatiles were largely lost leaving behind the suite of nonvolatile compounds that now characterize these meteorites.