Titan's thermosphere profile

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

The lunar sodium atmosphere: April–May 1998 ¹This article is part of a Special Issue that honours the work of Dr. Donald M. Hunten FRSC who passed away in December 2010 after a very illustrious career.

Atmospheric sodium at the Moon was observed for altitudes from the ground up to 1800 km from 18 April to 13 May 1998, a period including an entire lunar month. Because of bad weather, coverage was incomplete but we present the analysis of 36 spectra largely from near first and third quarter phases and passage through full moon. The apparatus used was the specially built clear aperture 16.5 cm, 203 cm focal length, Mt. Lemmon Lunar Coronagraph on Mt. Lemmon in the Catalina Mountains of Tucson, Arizona. Data are interpreted in terms of Chamberlain fits to the observed emission rate using both one equivalent temperature and two source components (with both cold and hot density distributions). The extent and equivalent temperatures of the exosphere during this period trended towards an extended coma with very little fraction in the thermally accommodated regime, even near the surface. Preliminary data–model comparisons suggest that these measurements are consistent with rates and spatial distributions expected from a photon-stimulated desorption source, although evidence for one, or possibly two, periods of notable meteoroid impact source might be present. A compilation of new and previously published observations illustrates an increased emission by sodium at third quarter over that of first quarter, a result that suggests that the dayside exospheric content increases, at least occasionally, following transit of the Moon through the Earth’s magnetosphere. </jats:p