| Popis: |
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 (C 2 H 2 -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 N 2 and CH 4 densities, together with qualiitative results from the aeronomic model and constraints from the Voyager IRIS observations in the methane v 4 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. |
