Shock Synthesis of Organic Molecules by Meteors in the Atmosphere of Titan

Shock energy applied to an atmosphere with the N₂/CH₄ composition of Saturn’s moon Titan will efficiently synthesize organic molecules. Meteors sufficiently large compared to the atmospheric mean free path will generate such shocks during atmospheric entry. But while the microscopic dust flux at Saturn had long been measured, the meteor flux in the millimeter- to meter-size range has been unknown, making it impossible to quantify reliably the importance of this effect. However, the Cassini spacecraft imaged the results of multiple meteoroid impacts on Saturn’s rings, allowing for the first time an empirical estimate to be made of the flux and size-frequency distribution of meteoroids at Saturn. We combine these results with an atmospheric entry model and measured shock production efficiencies for the N₂/CH₄ atmosphere appropriate to Titan, and calculate shock production rates for HCN, C₂H₂, C₂H₄, C₂H₆, and C₃H₈, as well as the resulting H₂ generation. We find that in the optimistic estimate for particle flux onto Titan, for example, HCN and C₂H₂ are produced at rates as high as 24% of the production rate due to UV photochemistry, suggesting that these particles are more important to Titan’s atmospheric chemistry than previous thought.