The deuterium/hydrogen distribution in chondritic organic matter attests to early ionizing irradiation

• Published in: Nature communications 2015-10, Vol.6 (1), p.8567-8567, Article 8567
• Main Authors: Laurent, Boris, Roskosz, Mathieu, Remusat, Laurent, Robert, François, Leroux, Hugues, Vezin, Hervé, Depecker, Christophe, Nuns, Nicolas, Lefebvre, Jean-Marc
• Format: Article
• Language: English
• Subjects: 704/2151/213; 704/2151/2809; 704/445/849; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary); Sciences of the Universe
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms9567

Primitive carbonaceous chondrites contain a large array of organic compounds dominated by insoluble organic matter (IOM). A striking feature of this IOM is the systematic enrichment in deuterium compared with the solar hydrogen reservoir. This enrichment has been taken as a sign of low-temperature ion-molecule or gas-grain reactions. However, the extent to which Solar System processes, especially ionizing radiation, can affect D/H ratios is largely unknown. Here, we report the effects of electron irradiation on the hydrogen isotopic composition of organic precursors containing different functional groups. From an initial terrestrial composition, overall D-enrichments and differential intramolecular fractionations comparable with those measured in the Orgueil meteorite were induced. Therefore, ionizing radiation can quantitatively explain the deuteration of organics in some carbonaceous chondrites. For these meteorites, the precursors of the IOM may have had the same isotopic composition as the main water reservoirs of the inner Solar System. The insoluble organic matter in primitive carbonaceous chondrites has a systematic large enrichment in deuterium and several hypotheses have been proposed to explain this. Here, the authors demonstrate that irradiation from the protosun could quantitatively explain the deuteration.