Characterization of Complex Organis (Tholins) Formed in Simulated Upper and Lower Atmospheres of Titan

Abstract

Titan is the sole satellite has dense atmosphere. It is of interest to know the possible formation mechanism of amino acids on Titan since it will give us suggestions on possible chemical evolution pathways to the primitive Earth. For the simulation of chemical reactions in upper and lower atmospheres of Titan, we synthesized tholin by plasma discharge and by proton irradiation from a gas mixture of nitrogen and methane. The product tholins were characterized. The Py-GC/MS results showed tholins contain aromatic and N-containing heterocyclic compounds. MALDI-Mass spectra of the tholins showed that both tholins gave peaks at m/z = 100-400, and had -CH2- units in them. Thus tholins formed by plasma discharge (PD) and those by proton irradiation (CR) might have similar structures each other. We hydrolyzed tholins and analyzed amino acids by HPLC. A number of amino acids were detected from both tholins. CR-tholins are superior to PD-tholins in energy yield. It is suggested that more tholins containing amino acid precursors are produced in the lower atmosphere of Titan than in the upper atmosphere.