Extraterrestrial Organic Chemistry as Recorded in Carbonaceous Chondrites

Abstract

Meteorites are ancient objects originating in the asteroid belt that have recorded a succession of chemical processes, starting from reactions in the interstellar medium, followed by reactions that accompanied the formation and evolution of the early solar system, and culminated with reactions during aqueous alteration in the meteorite parent bodies. One of the challenges in meteorite research is to decipher this record and to learn about interstellar formation processes as well as to conditions in the early solar system. The rare carbonaceous chondrites contain up to 3 weight-% of organic carbon, more than 80 percent of which is locked in an insoluble macromolecular material with the rest present in the form of extractable organic compound classes such as carboxylic acids, amino acids (including some with enantiomeric excesses) and polycyclic aromatic hydrocarbons (PAH). Both the components of the macromolecular material and the soluble organic compounds exhibit molecular and isotopic characteristics of abiotic synthetic processes that must have occurred in extraterrestrial environments. A combination of interstellar surface and gas-phase reactions, thermal and shock processes in the accretionary disk and alterations inside the asteroid parent body lead to the mixture of organic compounds observed in meteorites.