The role of subsurface ocean dynamics and phase transitions in forming the topography of icy moons

Abstract

The thermo-mechanical evolution of icy moons cannot be understood without taking into account the complex interaction between the solid ice crust and the liquid water ocean. This interaction is controlled by the heat flux from the ocean and the material properties of ice. In recent years, the mass and energy exchange between the crust and the ocean has been studied using two complementary approaches. While in the first approach, the heat flux from the ocean is governed by the internal dynamics of the ocean and is independent of the processes at the phase boundary, the other approach assumes that the heat flux from the ocean is controlled by variations in the melting temperature along the boundary and the role of the ocean in heat transfer is passive. Here we present a new method for modeling the heat transfer in the interior of icy moons. Our approach is based on solving the heat transfer equations simultaneously in the ice shell and the ocean, and is more general than the previous ones in that it consistently links the global ocean circulation with the melting temperature variations arising from the deformation of the ice-water phase boundary. The method is used to study the role of ocean circulation in the formation of surface and ice-water interface topographies. We show that the additional heat flux generated by variations in the melting temperature along the phase boundary counteracts the heat flux from the deep ocean but is not able to completely suppress it. The deep ocean heat flux is more reduced at high latitudes than near the equator, where the ocean circulation is dominated by strong zonal flows hampering the heat transfer in the meridional direction. Our simulations predict the shape and topography that are comparable in magnitude to those observed on Titan (∼500m) and explain the absence of a degree-2 sectoral component in the spherical harmonic expansion of Titan’s topography.