The Cooling Rate of a Liquid Shell in Titan's Interior

Abstract

Models describing the evolution of the primordial liquid layer in Titan's interior are presented using parameterized models. These models incorporate recent experimental data on the ammonia water phase diagram in the range [100 MPa–1 GPa] and recently published creep laws for ice I. Just after accretion, the thickening of the outer ice I layer is achieved by conduction. It seems likely that this outer shell becomes thick enough for solid-state convection to start about 200 myr after accretion. The temperature in the ice I outer shell cannot be larger than the melting temperature of the NH3–H2O liquid at the interface between the liquid layer and the ice I shell. As a result, the temperature in the ice I layer is much smaller than the melting temperature for ice I and the viscosity is too large to yield very vigorous convection and rapid cooling of the satellite. Moreover, this study suggests that the decay of the radioactive element content in the silicate rich inner core of the satellite keeps heating the core for 3 byr after the core overturn. If present after accretion, a liquid layer is likely to exist at the present time in Titan's interior. The thickness of the liquid layer does not vary much with time and its value depends only on the initial amount of ammonia.