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

• EUV stellar occultations by Titan's upper atmosphere from Cassini UVIS are analyzed.
• N2 and CH4 abundances are found using an optimized grid search retrieval algorithm.
• Species density profiles are calculated for altitudes between 1000 and 1400 km.
• Temperatures are derived from N2 scale height using an isothermal, hydrostatic model.
• Results are compared to INMS, and show significant variability between Titan flybys.

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. N2 and CH4 atmospheric profiles between 1000 and 1400 km are determined by using an optimized grid search retrieval method to provide a complete χ2χ2 surface for the two species abundance parameters at each level in the atmosphere. Kinetic temperature is extracted from hydrostatic analysis of the N2 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.