New perspectives on Titan's upper atmosphere from a reanalysis of the Voyager 1 UVS solar occultations

We have reanalyzed the Voyager 1 UVS solar occultations by Titan to expand upon previous analyses and to resolve inconsistencies that have been noted in the scientific literature. To do so, we have developed a detailed model of the UVS detector and improved both the data reduction methods and retrieval techniques. In comparison to the values previously determined by Smith et al. (1982, J. Geophys. Res. 87, 1351-1359) we find N-2 densities that are 25-60% higher, CH4 densities that are smaller by a factor of 3-7, and C2H2 densities that are. two orders of magnitude smaller. Our values for the thermospheric temperature are 153-158 K, which are approximately 20-40 K roughly colder than previous estimates. We also report the first-ever determination from Voyager UVS data of density profile information for C2H4, HCN, and HC3N. Finally, we present a simple engineering model that is consistent with our new results in the upper atmosphere and merges smoothly with the model of Yelle et al. (1997, in: HUYGENS Science, Payload and Mission, in: ESA SP, vol. 1177, pp. 243-256) in the lower atmosphere. Our results provide improved constraints for photochemical models and offer scientists a better understanding of Titan's upper atmosphere as we head into the Cassini era in the exploration of the saturnian system. (C) 2004 Elsevier Inc. All rights reserved.