Upper Limit on Titan's Atmospheric Argon Abundance

The Voyager 1 Ultraviolet Spectrometer (UVS) solar occultation data and a spectrum of the North Polar Region dayglow obtained during the Titan flyby are analyzed to infer an upper limit on the tropopause argon mixing ratio as a function of the tropopause CH₄ mixing ratio, ƒ_CH4. The spectroscopic upper limit on the tropopause Ar mixing ratio (mole fraction), ƒ_Ar, varies from 0.15 at ƒ_CH4 = 0.01 to 0.1 at ƒ_CH4 = 0.026 and decreasing to 0.08 at ƒ_CH4 = 0.05. When combined with the mean molecular mass constraint of E. Lellouch, A. Coustenis, D. Gautier, F. Raulin, N. Dubouloz, and C. Frere (1989, Icarus 79, 328-349), ƒ_Ar < 0.17 for any ƒ_CH4. The best fits to the solar occultation data require ƒ_CH4 ≥ 0.026; thus ƒ_Ar ≤ 0.1. Copyright 1993, 1999 Academic Press