The High Altitude Sunlit Titan Ionosphere

Cassini UVIS EUV and FUV spectrograph observations of high altitude sunlit Titan atmosphere emission show measurable emission at and above the exobase in electron excited nitrogen. The observations include emission from the N2 c4}' (0,0) and other bands, NI, and NII in the EUV, with the N2 LBH system NI, HI and CI in the FUV. The emission properties indicate the top of the atmosphere has a developed ionosphere maintained by deposition of soft magnetospheric electrons. Comparison of the sub-solar equatorial region at encounter T0 with the sunlit polar high altitude emission obtained at TA will be described through application of a nitrogen physical chemistry model fit to the data. At the altitudes examined here, extinction by CH4 is not measurable. Estimates of [N]/[N2] partioning has high as 0.07 have been obtained. The inferred dissociation rates will be used to provide a loss rate into the magnetosphere for atomic nitrogen.