Abstract
One of the features of Titan is dense atmosphere, mainly nitrogen and methane. Among various kinds of energy sources in Titan atmosphere, cosmic rays can penetrate deeply down to the surface, which could be most effective to produce organic compounds near the surface of Titan. We examined possible formation of bioorganic compounds in lower Titan atmosphere. A mixture of methane (5%) and nitrogen (95%) was irradiated with 3 MeV-protons from a van de Graaff accelerator. Solid product (CR tholin) was acid-hydrolyzed, and amino acids in the hydrolysate was quantified by HPLC and/or by GC/MS with a chiral column after derivatization by using chroloformate. MALDI-TOF-MS spctra implied that the CR tholin had -CH2- structure. Various amino acids were detected in CR tholin after acid hydrolysis: Indigenousness of amino acids was checked with their D/L ratio and/or by using 13CH4 as a carbon. Furthermore, recovering and hydrolyzing the synthesized CR tholin with H218O, amino acids that included 18O in the construction were identified by MALDI-TOF-MS. It was suggested that CR tholin could give amino acids after interaction with surface water ice and/or cometary water ice during meteoritic / cometary impacts.
