The spectrum of titan in the far-infrared and microwave regions |
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Authors: | Régis Courtin |
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Affiliation: | Department of Earth and Space Sciences, State University of New York, Stony Brook, New York 11794, USA |
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Abstract: | The pressure-induced absorptions of gaseous nitrogen (N2) and methane (CH4) are computed on the basis of the collisional lineshape theory of G. Birnhaum and E.R. Cohen [Canad. J. Phys.54, 593–602 (1976)]. Laboratory data at 300 and 124°K for N2 and at 296 and 195°K for CH4 are used to determine the collisional time constant and their temperature dependence. The spectrum of Titan from the microwave to the far-infrared region (0.1–600 cm?1) is then modeled using these opacities and a temperature profile of Titan's atmosphere derived from the Voyager 1 radio occultation experiment. The model atmosphere is composed of N2 and CH4, their relative proportions being determined by the vapor pressure law of CH4. A model with gaseous opacity alone is ruled out by the far-infrared observations. An additional opacity, thought to be associated with a methane cloud, is confirmed. The effective temperature of Titan is estimated at Te = 83.2 ± 1.4°K. |
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