Spectral Characterization of Carboxylic Acids, Amino Acids and Ammonium Salts as the Carriers of 3.2 µm Band of Comet 67P/Churyumov-Gerasimenko

Kurzfassung

The VIRTIS instrument (Visible InfraRed Thermal Imaging Spectrometer) aboard of the Rosetta spacecraft has collected hyperspectral images of the surface of comet 67P in the 0.4-5 μm range. It revealed a broad feature centered at 3.2 μm in the reflectance spectra of comet 67P/CG, which might be consistent with the presence of semi-volatile organics, also possibly detected by the COSAC and PTOLEMY instruments [1-4]. Carboxylic acids have been proposed as candidates as these molecules in the liquid form display a broad absorption band that fit that of the 3.2 μm band and carboxylic acids are also the main component in the soluble organic fraction in primitive meteorites, with several tens of carboxylic, dicarboxylic and hydroxylated acids identified so far [5]. In this study, we have focused on the experimental spectral characterization of the carriers of the band at ~ 3.2 μm with particular attention to amino acid and carboxylic acids whose spectral properties in the solid state are poorly known, as well as to the ammonium ion.