Titan Atmospheric Chemistry Revealed by Low-Temperature N2–CH4 Plasma Discharge Experiments

Chemistry in Titan’s N 2 -CH 4 atmosphere produces complex organic aerosols. The chemical processes and the resulting organic compounds are still far from understood, although extensive observations, laboratory, and theoretical simulations have greatly improved physical and chemical constraints on Titan’s atmosphere. Here, we conduct a series of Titan atmosphere simulation experiments with N 2 -CH 4 gas mixtures and investigate the effect of initial CH 4 ratio, pressure, and flow rate on the production rates and composition of the gas and solid products at a Titan relevant temperature (100 K) for the first time. We find that the production rate of the gas and solid products increases with increasing CH 4 ratio. The nitrogen-containing species have much higher yield than hydrocarbons in the gas products, and the N/C ratio of the solid products appears to be the highest compared to previous plasma simulations with the same CH 4 ratio. The greater degree of nitrogen incorporation in the low temperature simulation experiments suggests temperature may play an important role in nitrogen incorporation in Titan’s cold atmosphere. We also find that H 2 is the dominant gas product and serves as an indicator of the production rate of new organic molecules in the experiment, and that CH 2 NH may greatly contribute to the incorporation of both carbon and nitrogen into the solid particles. The pressure and flow rate affect the amount of time of the gas mixture exposed to the energy source and therefore impact the N 2 -CH 4 chemistry initiated by the plasma discharge, emphasizing the influence of the energy flux in Titan atmospheric chemistry.