The thermal structure of Triton's atmosphere: Pre‐Voyager models

We predict the existence of a relatively thick (several tens of mbar) N 2 ‐CH 4 atmosphere on Triton. As on Titan, we find that the organic haze produced by chemical reactions is the most significant factor affecting solar energy deposition. The production of haze material (∼ 10 −15 g cm −2 s −1 ) is obtained by scaling from the Titan value. Collision induced absorption, primarily N 2 ‐N 2 , is the dominant source of thermal infrared opacity. The troposphere is characterized by moist convection and the temperature lapse rate is determined by the saturation vapor relationship of N 2 (about 0.25 K km −1 ). Given Triton's present orbital parameters, one polar cap is receiving sunlight while the other cap is in darkness. Following Trafton (1984) we assume the sublimating pole extends poleward of 35° and treat volatile transport as an isobaric process. For nominal values of the surface albedo and emissivity of 0.3 and 0.4, respectively, we find the surface temperature is 59 K (pressure = 51 mb). There is a hot stratosphere ( T ≃ 130 K) similar to that on Titan due to absorption by the haze. The total opacity of the organic haze (or haze plus N 2 cloud) is ≤ 1.