Titan's latitudinal temperature distribution and seasonal cycle

Voyager IRIS brightness temperature measurements of Titan at a wavelength of 530 cm^-1 are crudely indicative of ground or lower tropospheric temperatures and indicate 93 K for the equator and 91 K for both northern and southern high latitudes. The symmetry between north and south is unexpected for the time of Voyager encounter (Northern Titan spring). We show that this near-symmetry can arise naturally in a model where the poles are "pinned" year-round at the dew point of CH₄-N₂ lakes or, more probably, a CH₄-N₂ rich surface layer on a deep ethane-rich ocean. For a polar temperature of 91 K, the model implies that the atmosphere contains somewhat less than 8% mole fraction of CH₄.