1208.4685 (Alessandro Morbidelli et al.)

NOTE: Explaining why the Uranian satellites have equatorial prograde orbits despite the large planetary obliquity    [PDF]

Alessandro Morbidelli, Kleomenis Tsiganis, Konstantin Batygin, Aurelien Crida, Rodney Gomes

We show that the existence of prograde equatorial satellites is consistent with a collisional tilting scenario for Uranus. In fact, if the planet was surrounded by a proto-satellite disk at the time of the tilting and a massive ring of material was temporarily placed inside the Roche radius of the planet by the collision, the proto-satellite disk would have started to precess incoherently around the equator of the planet, up to a distance greater than that of Oberon. Collisional damping would then have collapsed it into a thin equatorial disk, from which the satellites eventually formed. The fact that the orbits of the satellites are prograde requires Uranus to have had a non-negligible initial obliquity (comparable to that of Neptune) before it was finally tilted to 98 degrees.

View original: http://arxiv.org/abs/1208.4685