Convection-driven compaction as a possible origin of Enceladus's long wavelength topography

Abstract

The long wavelength surface topography of Enceladus shows depressions about 1 km in depth and ∼10² km wide. One possible cause of this topography is spatially variable amounts of compaction of an initially porous ice shell, driven by spatial variations in heat flux. Here, we show that the heat flux variations associated with convection in the shell can quantitatively match the observed features. We develop a simple model of viscous compaction that includes the effect of porosity on thermal conductivity, and find that an initial shell porosity of at least 20-25% is required to develop the observed topography over ∼1 Ga. This mechanism produces topographic depressions, not rises, above convective upwellings, and does not generate detectable gravity anomalies. Unlike transient dynamic topography, it can potentially leave a permanent record of ancient convective processes in the shallow lithospheres of icy satellites.