Suprathermal nitrogen atoms and molecules in Titan's corona

Abstract

Dissociation and dissociative ionization of molecular nitrogen by solar UV radiation and by photoelectrons and sputtering by magnetospheric ions are the main sources of translationally excited (hot) nitrogen atoms and molecules in the upper atmosphere of Titan. The Boltzmann equations describing the production, thermalization, and transport of suprathermal nitrogen atoms and molecules in Titan's upper atmosphere were solved using the Direct Simulation Monte Carlo method. Steady-state energy distribution functions for the hot nitrogen atoms and molecules were calculated vs. altitude in the thermosphere-exosphere transition region. The contribution of dissociation and atmospheric sputtering to the formation of Titan's hot nitrogen corona and to the escape flux into the Saturnian magnetosphere are described using the calculated energy distribution functions. It is shown that photo-dissociation dominates and, therefore, the principal ejecta are N atoms.