Titan's thermosphere profile
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We have reexamined the aeronomic model of Titan's thermosphere by A.J. Friedson and Y.L. Yung (J. Geophys. Res. 89, A1, 85-90). Our computations disagree with theirs on the evaluation of the solar heating profile. We attribute this discrepancy to a numerical error in their code. Moreover, new measurements on acetylene relaxation incite us to reconsider also their formulation of the (C2H2-dominated) infrared cooling. Once these factors are corrected, resolution of the heat transfer equation leads to a profile in severe conflict with the Voyager UVS temperature measurement at 1265 km from Titan's surface. A possible way to solve this problem is to assume very low (∼0.15-0.20) heating efficiencies. Simple considerations on the UVS measurements of temperature and N2 and CH4 densities, together with qualiitative results from the aeronomic model and constraints from the Voyager IRIS observations in the methane v4 band allow one to infer the general shape of Titan's atmosphere thermal profile. Possible features of this profile are a quasi-isothermal region between 200 and 400 km and a 135°K mesopause at 800 km.
CitationLellouch, E.; Hunten, D.M.; Kockarts, G.; Coustenis, A. (1990). Titan's thermosphere profile. , Icarus, Vol. 83, Issue 2, 308-324, DOI: 10.1016/0019-1035(90)90070-P.