Energetic photon irradiation of carbonaceous icy grains–laboratory studies on the interstellar ice-dust interface in star-forming regions

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In the dense interstellar medium, cosmic dust grains are covered by a molecular ice layer. These grains consisting of a refractory and a volatile component are expected to be continuously irradiated by energetic photons. Thin molecular ice layers of about 10 nm on dust grains can be penetrated by photons. They can interact with the refractory dust material activating photon-induced reactions in the ice/dust material and at the ice-dust interface. The proposed project between the Laboratory Astrophysics and Cluster Physics Group in Jena and the Photoprocessing Spectroscopy Laboratory in Taiwan is dedicated to the investigation of photon-induced modifications of ice-dust grains in the interstellar medium and in star-forming regions. The interface between ice and dust is characterized by a large contact area due to the small sizes of particles and the high porosity of the dust agglomerates. The joint research project under the DFG-MOST program is established to study the ice-dust interface processing triggered by energetic photons comprising vacuum ultraviolet photons (E <10.9 eV), extreme ultraviolet photons (E=11-40 eV), and soft X-ray photons (E= 80-1200 eV). This research will address three different objectives namely the possible interactions of radicals with carbonaceous dust surfaces leading to the erosion of the material, the formation of organic and prebiotic molecules at the ice-dust interface and the effect of energetic photons on the composition and structure of the refractory dust materials. We will include amorphous and hydrogenated amorphous carbon nanoparticles with fullerene-like structural subunits and silicate/carbon mixtures. Systematic experimental studies as a function of typical interstellar parameters such as temperature and photon energy will be performed on dust analogs covered by pure ices including H2O, NH3, CH4, H2S, N2 and O2. The outcome of this project on energetic grain/ice processing will improve our knowledge on the interstellar grain evolution and will help to better understand the ingredients of planetary systems and planets. It will also be important for Astrochemistry, Astrobiology, and (Exo-)Planetary Science. The research project is an innovative and timely preparation of the upcoming James Webb Space Telescope expected to be launched in 2021, which will reveal the details of interstellar ice and dust in exceptionally high IR spectral resolution and sensitivity.