Physico-chemical models of the internal structure of partially differentiated Titan

Abstract

We analyze models of the internal structure of Titan, a large icy satellite of the Saturn system. Calculations are carried out using information on the mass, mean density, moment of inertia, orbital parameters, and elastic properties of the satellite obtained by the Cassini–Huygens mission, as well as geochemical data on the composition of chondrite materials, equations of state of water and ices I, III, V, VI, and VII, and thermodynamic models for conductive heat transfer in the outer icy crust and of global convection in the interior zones of the satellite. The analysis of the models shows that models of partially differentiated Titan are most consistent; they include an outer water–ice shell, an intermediate ice–rock mantle, and an inner rock–iron core. It is shown that for the models of this type the maximum thickness of the water–ice shell is 460–470 km; it can be composed of an outer conductive crust of Ih ice 80–110 km thick and a subsurface water ocean 200–300 km deep. The maximum radius of the central rock–iron core of Titan can reach ~1300 km. The thickness of Titan’s ice–rock mantle does not exceed 2100 km at a density of 1.22–2.64 g/cm³. The model of partially differentiated Titan is feasible in the moment of inertia range of 0.312 < I/MR² < ~0.350.