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Optical alteration of complex organics induced by ion irradiation:: 1. Laboratory experiments suggest unusual space weathering trend |
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| Authors: | Lyuba Moroz Giuseppe Baratta Larissa Starukhina Maria Antonietta Barucci Elisa Distefano |
| Institution: | a German Aerospace Center (DLR), Rutherfordstr. 2, D-12489 Berlin, Germany b INAF, Catania Astrophysical Observatory, Via S. Sofia 78, Catania I-95123, Italy c Astronomical Institute of Kharkov National University, Sumskaya 35, Kharkov 61022, Ukraine d INAF, Rome Astrophysical Observatory, Via Frascati 33, I-00040 Monteporzio Catone, Rome, Italy e Paris Observatory, 5 Pl. Jules Janssen, F-92195 Meudon Principal Cedex, France |
| Abstract: | Most ion irradiation experiments relevant to primitive outer Solar System objects have been performed on ice and silicate targets. Here we present the first ion irradiation experiments performed on natural complex hydrocarbons (asphaltite and kerite). These materials are very dark in the visible and have red-sloped spectra in the visible and near-infrared. They may be comparable in composition and structure to refractory organic solids on the surfaces of primitive outer Solar System objects. We irradiated the samples with 15-400 keV H+, N+, Ar++, and He+ ions and measured their reflectance spectra in the range of 0.3-2.5 μm before ion implantation and after each irradiation step. The results show that irradiation-induced carbonization gradually neutralizes the spectral slopes of these red organic solids. This implies a similar space weathering trend for the surfaces of airless bodies optically dominated by spectrally red organic components. The reduction of spectral slope was observed in all experiments. Irradiation with 30 keV protons, which transfers energy to the target mostly via electronic (inelastic) collisions, showed lower efficiency than the heavier ions. We found that spectral alteration in our experiments increased with increasing contribution of nuclear versus electronic energy loss. This implies that nuclear (elastic) energy deposition plays an important role in changing the optical properties of irradiated refractory complex hydrocarbon materials. Finally, our results indicated that temperature variations from 40 K to room temperature did not influence the spectral properties of these complex hydrocarbon solids. |
| Keywords: | Radiation chemistry Organic chemistry Spectroscopy |
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