Composition of Titan's upper atmosphere from Cassini UVIS EUV stellar occultations

Identifying seasonal and spatial variability in Titan's atmospheric structure is a key factor in improving theoretical models of atmospheric loss and understanding the physical processes that control the loss rate. In this work, the extreme ultraviolet (EUV) stellar occultation lightcurves from the Cassini Ultraviolet Imaging Spectrograph (UVIS) experiment are analyzed. N-2 and CH4 atmospheric profiles between 1000 and 1400 km are determined by using an optimized grid search retrieval method to provide a complete chi(2) surface for the two species abundance parameters at each level in the atmosphere. Kinetic temperature is extracted from hydrostatic analysis of the N-2 profiles, and indicates a high level of variability related to energy deposition in the upper atmosphere. These results are compared to in situ measurements by the Ion Neutral Mass Spectrometer (INMS), which also probes this region of Titan's atmosphere. (C) 2013 Elsevier Ltd. All rights reserved.