Photo and thermochemical evolution of astrophysical ice analogs as a source for soluble and insoluble organic materials in Solar System minor bodies

Pierre de Marcellus, Aurelien Fresneau, Rosario Brunetto, Gregoire Danger, Fabrice Duvernay, Cornelia Meinert, Uwe J. Meierhenrich, Ferenc Borondics, Thierry Chiavassa, and Louis Le Sergeant d’Hendecourt

MNRAS doi:10.1093/mnras/stw2292
First published online September 12, 2016


“Soluble and Insoluble Organic Matter is a key feature of primitive carbonaceous chondrites. We observe the formation of organic materials in the photo-thermochemical treatment of astrophysical ices in the laboratory. Starting from a low vacuum ultraviolet (VUV) irradiation dose on templates of astrophysical ices at 77 K, we obtain first a totally soluble form of organic matter at room temperature. Once this organic residue is formed, irradiating it further in vacuum results in the production of a thin altered dark crust on top of the initial soluble one. The whole residue is studied here by non-destructive methods inducing no alteration of samples, visible microscopy and mid-infrared (micro)-spectroscopy. After water extraction of the soluble part, an insoluble fraction remains on the sample holder which provides a largely different infrared spectrum when compared to the one of the soluble sample. Therefore, from the same VUV and thermal processing of initial simple ices, we produce first a soluble material from which a much larger irradiation dose leads to an insoluble one. Interestingly, this insoluble fraction shows some spectral similarities with natural samples of Insoluble Organic Matter (IOM) extracted from two meteorites (Tagish Lake and Murchison), selected as examples of primitive materials. It suggests that the organic molecular diversity observed in meteorites may partly originate from the photo and thermal processing of interstellar/circumstellar ices at the final stages of molecular cloud evolution toward the build-up of our solar system. “