  The origin of the Uranian satellite system remains uncertain. The four major
satellites have nearly circular, co-planar orbits and the ratio of the
satellite system and planetary mass resembles Jupiter's satellite system,
suggesting the Uranian system was similarly formed within a disk produced by
gas co-accretion. However, Uranus is a retrograde rotator with a high
obliquity. The satellites orbit in its highly tilted equatorial plane in the
same sense as the planet's retrograde rotation, a configuration that cannot be
explained by co-accretion alone. In this work we investigate the first stages
of the co-accretion + giant impact scenario proposed by Morbidelli et al.
(2012) for the origin of the Uranian system. In this model, a satellite system
formed by co-accretion is destabilized by a giant impact that tilts the planet.
The primordial satellites collide and disrupt, creating an outer debris disk
that can re-orient to the planet's new equatorial plane and accrete into
Uranus' 4 major satellites. The needed reorientation out to distances
comparable to outermost Oberon requires that the impact creates an inner disk
with $\ge 1\%$ of Uranus' mass. We here simulate giant impacts that
appropriately tilt the planet and leave the system with an angular momentum
comparable to that of the current system. We find that such impacts do not
produce inner debris disks massive enough to realign the outer debris disk to
the post-impact equatorial plane. Although our results are inconsistent with
the apparent requirements of a co-accretion + giant impact model, we suggest
alternatives that merit further exploration.
