High-temperature shock formation of N₂ and organics on primordial Titan

Abstract

Titan's atmosphere is composed primarily of N₂ with a little methane and other organic molecules. But theoretical models suggest that the initial form of nitrogen in Titan's atmosphere may have been NH₃. We have investigated the possible importance of strong shocks produced during high-velocity impacts accompanying the late stages of accretion as a method for converting NH₃ to N₂. To simulate the effects of an impact in Titan's atmosphere we have used the focused beam of a high-power laser, a method that has been shown to simulate shock phenomena. For mixtures of 10%, 50% and 90% NH₃ (balance CH₄) we obtained yields of 0.25, 1, and 6 × 10¹⁷ molecules of N₂ per joule, respectively. We also find that the yield of HCN is comparable to that for N₂. In addition, several other hydrocarbons are produced, many with yields in excess of theoretical high-temperature-equilibrium models. The above yields, when combined with models of the satellite's accretion, result in a total N₂ production comparable to that present in Titan's atmosphere and putative ocean.