Resurfacing of Uranus' Moon Miranda by Convection: Understanding the Influence of Core Size on Convection Geometry

Abstract:

Miranda is a small icy moon of Uranus. Three remarkable regions of intense deformation, called coronae, are visible in southern hemisphere of Miranda. Coronae are ~200 km wide, and are surrounded by concentric, sub-parrallel lineations, that have been interpreted as extensional tectonic and volcanic landforms.

Here we test the hypothesis coronae formed as a result of convection in Miranda’s ice mantle during an episode of tidal heating. Using numerical models of spherical convection, we show that if Miranda’s surface is weak, sluggish lid convection can occur, which simultaneously generates the concentric deformation patterns observed in the coronae, the inferred thermal gradient predicted by models of flexure, and the approximate number of plumes necessary to form the coronae.

We have tested the influence of core size on convection geometry. For basal Rayleigh numbers between 10^5 and 10^8, and for effective viscosity contrasts less than 10^4, we found that low-order convection patterns only remain stable for core radii less than half the satellite radius. This suggests that low-order convection patterns may be more likely to develop in planets and satellites with small cores, however we find that the distribution of tidal heating within icy satellites also strongly influences convection geometry.