Electromagnetic induction in the icy satellites of Uranus

Abstract

The discovery of subsurface oceans in the outer solar system has transformed our perspective of ice worlds and has led to consideration of their potential habitability. The detection and detailed characterisation of induced magnetic fields due to these subsurface oceans provides a unique ability to passively sound the conducting interior of such planetary bodies. In this paper we consider the potential detectability of subsurface oceans via induced magnetic fields at the main satellites of Uranus. We construct a simple model for Uranus' magnetospheric magnetic field and use it to generate synthetic time series which are analysed to determine the significant amplitudes and periods of the inducing field. The spectra not only contain main driving periods at the synodic and orbital periods of the satellites, but also a rich spectrum from the mixing of signals due to asymmetries in the uranian planetary system. We use an induction model to determine the amplitude of the response from subsurface oceans and find weak but potentially-detectable ocean responses at Miranda, Oberon and Titania, but did not explore this in detail for Ariel and Umbriel. Detection of an ocean at Oberon is complicated by intervals that Oberon will spend outside the magnetosphere at equinox but we find that flybys of Titania with a closest approach altitude of 200 km would enable the detection of subsurface oceans. We comment on the implications for future mission and instrument design.