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Thermochemical modeling and shock-tube experiments show that shocks appliedto N$_2$/CH$_4$ gas mixtures can synthesize organic molecules. Sufficientlylarge, hypersonic meteoroids entering the atmosphere of Saturn's moon Titanshould therefore drive organic chemistry. To do so meteoroids must besufficiently large compared to the atmospheric mean free path at a givenaltitude to generate shocks, and deposit enough energy per path length toproduce temperatures high enough to excite and dissociate the relevantmolecules. The Cassini spacecraft imaged multiple meteoroid impacts on Saturn'srings, allowing for the first time an empirical estimate to be made of the fluxand size-frequency distributions of meteoroids in the millimeter-to-meter sizerange. We combine these results with an atmospheric entry model andthermochemical and experimental shock production efficiencies for N$_2$/CH$_4$atmospheres and calculate the shock production rates for HCN, C$_2$H$_2$, andC$_2$H$_4$ as well as the resulting H$_2$ generation. We find that meteoroidsmay be producing these molecules at as much as $\sim$1% the production rate ofphotochemistry driven by UV photons, and may be depositing more energy thanmagnetospheric ions and 90-100 nm UV photons. Moreover, these meteoroidsproduce these organic molecules hundreds of kilometers lower in Titan'satmosphere than the relevant UV photons and magnetospheric ions penetrate, withpeak production occurring between 200 and 500 km altitudes, i.e., at theobserved haze layer. Meteoroid-driven shock generation of molecules maytherefore be crucial to understanding Titan's atmospheric chemistry.

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