Heating Titan's upper atmosphere

Abstract

A detailed analysis of the mechanisms heating Titan's neutral atmosphere is provided. Two primary sources of incoming energy, the solar photons and the energetic electrons from Saturn's magnetosphere, are taken into account. The processes studied include the excitation of atmospheric molecules by electron impact, suprathermal electron heating, and the energy release through ion and neutral exothermic chemistry. The redistribution of heat by suprathermal particles throughout the atmosphere is also considered and calculated using a two-stream model. Local time-dependent heating rate profiles are presented. Exothermic chemistry is found to be the dominant source of heat, with electron-impact excitation and suprathermal electron heating becoming significant at high altitudes. Large variations in local peak amplitudes were found, varying between ≃3 × 10^-10 erg cm^-3s^-1 at 990 km and zenith angle 62° and ≃7 × 10^-12 erg cm^-3s^-1 at 940 km and zenith angle 165°. Neutral heating efficiency profiles averaged with respect to local time at the fixed latitudes of 38.8° N and 73.7° N are presented, with mean values of ≃25 ± 15% and 23 ± 19%, respectively.