Photolysis of Cometary Organic Dust Analogs on the EXPOSE-R2 Mission at the International Space Station

Abstract

We describe the results obtained on a set of organic samples that have been part of the experiment "Photochemistry on the Space Station (PSS)" on the EXPOSE-R2 mission conducted on the EXPOSE-R facility situated outside the International Space Station (ISS). The organic samples were prepared in the Catania laboratory by 200 keV He<SUP>+</SUP> irradiation of N<SUB>2</SUB>:CH<SUB>4</SUB>:CO icy mixtures deposited at 17 K, on vacuum UV (VUV) transparent MgF<SUB>2</SUB> windows. This organic material contains different chemical groups, including triple CN bonds, that are thought to be of interest for astrobiology. It is widely accepted that materials similar to that produced in the laboratory by ion irradiation of frozen ices could be present in some astrophysical environments such as comets. Once expelled from comets, these materials are exposed to solar radiation during their interplanetary journey. In the young Solar System, some of these processed materials could have reached early Earth and contributed to its chemical and prebiotic evolution. The samples were exposed for 16 months to the unshielded solar UV photons. It was found that, if an interplanetary dust particle (IDP) containing organic material (50% vol) is large enough (>20-30 μm), relevant chemical groups, such as those containing the CN triple bond, can survive for many years (>10<SUP>4</SUP> years) in the interplanetary medium.