In Search of Subsurface Oceans within the Uranian Moons

The Galileo mission to Jupiter discovered magnetic signatures associated with hidden sub-surface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within these moons and are driven by Jupiter’s strong time-varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies as both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager 2 visited the ice giants in the 1980s, it did not pass close enough to any of the major moons to detect magnetic induction signatures. However, the Voyager flyby revealed that some of these ice giant moons exhibit surface features that hint at geologically recent activity and the possibility that these objects may harbor sub-surface oceans. Future missions to the ice giants may therefore be capable of discovering hidden sub-surface oceans, thereby adding to the family of known “ocean worlds” in our solar system. Here, we assess magnetic induction as a technique for investigating sub-surface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity, and depth, as well as ionospheric conductance. The results reported here demonstrate the possibility of single-pass ocean detection and characterization at the moons Miranda, Ariel, and Umbriel, and provide guidance to required magnetometer performance and trajectory design for future missions to Uranus.