Compositions and Interior Structures of the Large Moons of Uranus and
Implications for Future Spacecraft Observations
Abstract
The five large moons of Uranus are important targets for future
spacecraft missions. To motivate and inform the exploration of these
moons, we model their internal evolution, present-day physical
structures, and geochemical and geophysical signatures that may be
measured by spacecraft. We predict that if the moons preserved liquid
until present, it is likely in the form of residual oceans less than 30
km thick in Ariel, Umbriel, Titania, and Oberon. The preservation of
liquid strongly depends on material properties and, potentially, on
dynamical circumstances that are unknown. Miranda is unlikely to
preserve liquid until present unless it experienced tidal heating a few
tens of million years ago. The triaxial shapes estimated from Voyager 2
data for Miranda and Ariel further support the prospect that these moons
are internally differentiated with a rocky core and icy shell. We find
that since the thin residual layers may be hypersaline, their induced
magnetic fields could be detectable by future spacecraft-based
magnetometers. However, if the ocean is maintained primarily by ammonia,
and thus well below the water freezing point, then its electrical
conductivity may be too small to be detectable by spacecraft. Lastly,
our calculated tidal Love number (k2) and
dissipation factor (Q) are consistent with the
Q/k2 values previously inferred from
dynamical evolution models. In particular, we find that the low
Q/k2 estimated for Titania supports the
hypothesis that Titania currently holds an ocean.