A Hypothesis for a Unified Mechanism of Formation and Enantioenrichment of Polyols and Aldaric, Aldonic, Amino, Hydroxy and Sugar Acids in Carbonaceous Chondrites

Abstract

Carbonaceous chondrites are a type of meteorite with a high organic content, which formed early in the history of the solar system. In addition to large amounts of insoluble high molecular weight organic polymer, they contain a variety of small organic molecules such as polycyclic aromatic hydrocarbons, polyols and aldaric, aldonic, amino, hydroxy and sugar acids, among others. Intriguingly, some of the amino acids and hydroxy acids have been found to display a chiral bias. The types of compounds present, their isotopic distributions and relative abundances may provide clues to the mechanisms by which they were synthesized in meteorite parent bodies. A unified set of mechanisms which may explain some of these properties is presented here. It involves simple addition reactions of cosmically abundant 1-carbon compounds such as HCHO and HCN undergoing well-established aqueous chemistry. Although aqueous processes could amplify and pass a chiral bias from one type of compound to another, circularly polarized light or another pre-accretion mechanism may have been required to initiate the chiral bias observed. Most of the small organic molecules present in these meteorites (90 to > 99% by number) to date remain unidentified; these mechanisms may provide a framework for identifying them.