Photochemistry and Eddy Mixing in Pluto’s atmosphere

Abstract:

We present a photochemical model of Pluto’s atmosphere that includes complete chemistry of hydrocarbons and nitriles, and apply this model to the interpretation of Alice ultraviolet observations during the New Horizons flyby in July 2015. This model self-consistently calculates the production, transport, and condensation of hydrocarbons from the surface to the exosphere. New features of the model include the condensation of molecules and their sublimation back into the gas. The Alice observations of C₂H₂ and C₂H₄ provide strong constraints on the rate of eddy mixing in the altitude region 100-600 km altitude region. Inferred mixing rates are low, consistent with slow downward transport of long-lived photochemical products to Pluto’s lower atmosphere where loss by condensation occurs. We present an interpretation of the observed hydrocarbons as a test of our understanding of Pluto’s atmosphere photochemistry.