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M.L. Delitsky, A.L. Lane (Jet Propulsion Laboratory), T.T. Tidwell, H. Henry-Riyad (University of Toronto)
Titan's atmosphere contributes nitrogen atoms and ions to the Saturnian magnetosphere. These ions have inward motion towards Saturn and should impact the inner satellites, thereby inducing a complex nitrogen oxides chemistry in the surfaces via their interaction with the water ice present. Species formed may include NO, NO2, NO3, HNO2, HNO3, NH2OH, HNO, NH, NH2, N2O, HNNO, and N2. If the surfaces also include CO2, then other species that may be formed as a result of N+ impact into H2O/CO2 ice will be HNCO, NCO and R-OCN.
Successive reaction of HNCO with H and CO (which occur in irradiated H2O/CO2 ice) could lead to the smallest amino acid, glycine, in only 5 steps. Addition of CO to HNCO with successive hydrogenation of the oxygen atoms forms an -OH group with a C=O bond still present. Migration of the OH onto the C=O carbon yields a carboxylic acid group (-COOH). The HNCO -> Glycine conversion utilizes only simple and exothermic addition and rearrangement reactions. Both H and CO would be mobile in the water/CO2 ice crystal at the temperatures on the Saturnian satellites. Every step in the sequence is calculated to be exothermic, and the entire sequence is exothermic by a total of 231 kcal/mole. Therefore these sequences may occur under the temporary non-equilibrium conditions resulting from high-energy particle impact and subsequent residual heating.
Glycine has its own radiolysis products, such as CHOCOOH (glyoxylic acid), CH3NH2 (methyl amine), HCHO, NH3, H2O2, and H2. Formation of higher-order amino acids, such as alanine and aminobutyric acids, might also occur, from solid-phase radiolysis or gas-phase ionic synthesis of combinations of some of the smaller molecules in the sequence.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.