Masses of the satellites of Uranus

A marked dichotomy in the density distribution of the Uranian satellites has been observed. The densities of Ariel and Umbriel are similar to those of the inner satellites of Saturn, and are consistent with a composition of 40 percent rock and 60 percent water ice, while Titania and Oberon appears to have much higher densities. It is argued here that the problem posed by this density distribution arises from a misunderstanding of the orbital dynamics and may be imaginary. It is also shown that the observed eccentricities of the inner satellites, Ariel and Miranda, may be partly forced by the outer satellites, and that these forced eccentricities may be maintained despite strong tidal damping.