The uranian system consists of the ice giant planet Uranus, its rings, and at least 27 moons. The five major moons — Miranda, Ariel, Umbriel, Titania, and Oberon — are of interest because they might host liquid water, which makes them targets for spacecraft exploration to determine the extent of habitability in the solar system.

Julie Castillo-Rogez of NASA’s Jet Propulsion Laboratory led a study to inform such future exploration by building thermochemical models to investigate the internal evolution of these moons and the conditions under which subsurface oceans could be preserved. These models were constrained by reanalysis of Voyager 2 observations of the uranian system and utilized new insights into the geophysics and geochemistry of icy bodies from recent missions such as Cassini, New Horizons, and Dawn. The team found that while Miranda is unlikely to currently host liquid, oceans up to 30 kilometers thick may be present in Ariel and Umbriel, and oceans up to 50 kilometers thick may be present in Titania and Oberon. Retention of a liquid layer depended on material properties (e.g., a porous crust would better insulate the interior) and possibly on tidal heating from orbital dynamics interactions between bodies.

The Uranus Orbiter and Probe (UOP) mission concept was selected as the highest priority flagship-class mission by the National Academy of Science’s Planetary Science and Astrobiology Decadal Survey. A goal of this study was to quantify observations that a mission like UOP could make to improve our understanding of the evolution and current state of the uranian moons. These include determining their shapes and moments of inertia, which would provide information on internal structures; looking for evidence of induced magnetic fields, the presence of which would suggest subsurface oceans; and looking for exposures of deep material via impacts or cryovolcanism, which would reveal compositions of the interior, possibly including materials from the proposed oceans. READ MORE