Analytic investigation of climate stability on Titan: sensitivity to volatile inventory

We develop a semiempirical grey radiative model to quantify Titan's surface temperature as a function of pressure and composition of a nitrogen-methan e-hydrogen atmosphere, solar flux and atmospheric haze. We then use this mo del, together with non-ideal gas-liquid equilibrium theory to investigate t he behavior of the coupled surface-atmosphere system on Titan. We find that a volatile-rich Titan is unstable with respect to a runaway greenhouse-sma ll increases in solar luminosity from the present value can lead to massive increases in surface temperature. If methane has been photolyzed throughou t Titan's history, then this runaway can only be avoided if the photolytic ethane is removed from the surface-atmosphere system. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.