Organic chemistry induced by corona discharges in Titan’s troposphere: Laboratory simulations

Abstract

One of the most interesting questions about Titan is the possibility of finding evidence of electrical activity that could lead to some chemical transformations of its nitrogen and methane rich atmosphere. Following the proposal by Navarro-González and Ramírez, (Navarro-González, R., Ramírez, S.I., Corona discharge of Titan’s troposphere, Adv. Space Res. 19 (7), 1121–1133, 1997.) on the likelihood of the presence of electrical discharges developing in Titan’s low atmosphere, we present here the energy yields of 24 hydrocarbons and six nitriles synthesized by positive and negative corona discharges from mixtures of methane and nitrogen at 298 K. We have investigated the effect of the methane mixing ratio (0.02–0.1), gas pressure (100–1000 mbar), the electrical polarity of the corona discharge and the design of the reactor on the energy yields of the identified gas-phase organic products. Our results show that the synthesis of molecules containing 2 or 3 carbon atoms is slightly favoured by an initial gas pressure of 1000 mbar. Ethane and methanenitrile have the highest energy yields at a methane mixing ratio of 0.05. These molecules could be the precursors of heavier hydrocarbons and nitriles identified in our experiments at higher exposure times. Saturated hydrocarbons and nitriles have higher energy yields in positive corona discharge. We present and discuss these results in the frame of the Cassini–Huygens mission.