Analysis of measurements of the H2 density in Saturn's equatorial thermosphere indicates temperatures from 340 to 370 K. The deepest measurements, obtained during Cassini's final plunge into the atmosphere, measure the thermospheric temperature profile. The measurements are well fit by a Bates profile with an exospheric temperature of 354 K and a temperature gradient at 1.2 × 10−4 Pa of 0.4 K/km, corresponding to a thermal conduction flux of 7.3 × 10−5 W/m2. The helium profiles are consistent with diffusive equilibrium. The CH4 profiles are not in diffusive equilibrium but instead have a roughly constant mixing ratio relative to H2. We interpret this as the signature of a downward external flux of ∼1013 m−2 s−1. Saturn's rings are the most likely source of this external material.
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)