Other
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.4702l&link_type=abstract
American Astronomical Society, DPS meeting #39, #47.02; Bulletin of the American Astronomical Society, Vol. 39, p.505
Other
Scientific paper
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 have been made through application of a nitrogen physical chemistry model. The sub-solar spectra show the presence of scattered solar flux at wavelengths > 155 nm at altitudes extending above 1000 km, consistent with the aerosol extinction measurements in stellar occultations reported by Liang et al., 2007, and Shemansky et al., 2007. Derived extinction by CH4 in fits to the data is consistent with the UVIS occultation results. Model calculations fitting the observed non LTE atomic nitrogen emission show that more than 50% of the steady state NI population is in the 2Do state. Estimates of [N]/[N2] partitioning has high as 0.07 have been obtained. Heating in the ionosphere at 1300 km is assumed to be mainly through dissociation of N2. From the N2 profile we obtain 3.7 X 10-3 ergs cm-2 s-1, compared to 8.7 X 10-4 ergs cm-2 s-1 for photoionization. The total dissociation rate of N2 is estimated at 109 cm-2 s-1 compared to 2.2 X 108 cm-2 s-1 for solar photoionization. Atomic nitrogen loss rate into the magnetosphere is estimated to be 2. X 1026 atoms s-1.
This work is supported by the Cassini Program and NASA PATM.
Liu Xianming
Shemansky Don E.
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