Searching for subsurface oceans on the moons of Uranus using magnetic induction

Abstract:

Icy moons around the ice giant planets may contain subsurface oceans. The habitability of such oceans may depend on the thicknesses of these oceans and of the overlying ice shells. These oceans can be detected and characterized using measurements of magnetic fields generated by electrical currents induced by ambient time-varying magnetic fields. We explore the possibility of detecting and characterizing subsurface oceans among the 27 moons in the Uranus system using spacecraft magnetometry measurements from flybys and orbiters. We focus in particular on the five major moons—Miranda, Ariel, Umbriel, Titania, and Oberon—whose surfaces exhibit geological evidence for cryovolcanism and endogenic volcanic activity (see Voyager 2 image in figure). We find that the magnetic field experienced by each moon varies as a consequence of Uranus’s rotation and the moons’ orbital motions (along with other processes) with amplitudes ranging from as low as >3 nT at Oberon up to >300 nT at Miranda (see figure). If these bodies contain oceans with sufficient depths (e.g., >~10-100 km) and conductivities (e.g., like that of Earth’s ocean), the induced surface fields should have amplitudes exceeding the typical ~1 nT sensitivity of spacecraft fluxgate magnetometry investigations. Furthermore, magnetic field signals at the moons with amplitudes above this threshold span a wide range of significant frequencies ranging from ~10^-7 to 10^-4 Hz. This rich range of frequencies should enable long-term measurements by a Uranus orbiter to constrain key ocean parameters for each moon including the ocean and ice thickness and salinity.