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R.J. Vervack, Jr. (JHU/Applied Physics Lab), B.R. Sandel (LPL/Univ. Arizona)
The Voyager 1 Ultraviolet Spectrometer (UVS) observations are the only direct measurements we have of Titan's upper atmosphere. Previous analysis of the two UVS solar occultations yielded densities for N2, CH4, and C2H2, as well as the thermospheric temperature. These results serve as the upper atmospheric boundary conditions in models of Titan's atmosphere; however, there are discrepancies between the observations and models, and the previous analysis itself is known to be internally inconsistent.
We have undertaken a reanalysis of the UVS solar occultations to resolve these differences and to extract the maximum amount of information from the data. In so doing, we have developed a detailed model of the UVS detector and an analysis method tailored to retrieving multiple species from an occultation of a finite-sized source such as the sun. Our analysis has yielded density profiles for nine species in Titan's upper atmosphere and a new measurement of the thermospheric temperature. We find higher N2 densities and lower CH4 and C2H2 densities than those previously determined. We also find a thermospheric temperature of 150-155 K instead of 176-196 K as in the early analysis. Densities for C2H4, C2H6, C4H2, C2N2, HCN, and HC3N are retrieved in the upper atmosphere for the first time. These results provide improved and expanded constraints for the atmospheric models and should provide scientists with a better view of Titan's upper atmosphere, which is important in planning for the upcoming Cassini mission.
The author(s) of this abstract have provided an email address for comments about the abstract: Ron.Vervack@jhuapl.edu