  We perform a suite of smoothed particle hydrodynamics simulations to
investigate in detail the results of a giant impact on the young Uranus. We
study the internal structure, rotation rate, and atmospheric retention of the
post-impact planet, as well as the composition of material ejected into orbit.
Most of the material from the impactor's rocky core falls in to the core of the
target. However, for higher angular momentum impacts, significant amounts
become embedded anisotropically as lumps in the ice layer. Furthermore, most of
the impactor's ice and energy is deposited in a hot, high-entropy shell at a
radius of ~3 Earth radii. This could explain Uranus' observed lack of heat flow
from the interior and be relevant for understanding its asymmetric magnetic
field. We verify the results from the single previous study of lower resolution
simulations that an impactor with a mass of at least 2 Earth masses can produce
sufficiently rapid rotation in the post-impact Uranus for a range of angular
momenta. At least 90% of the atmosphere remains bound to the final planet after
the collision, but over half can be ejected beyond the Roche radius by a 2 or 3
Earth mass impactor. This atmospheric erosion peaks for intermediate impactor
angular momenta (~3*10^36 kg m^2 s^-1). Rock is more efficiently placed into
orbit and made available for satellite formation by 2 Earth mass impactors than
3 Earth mass ones, because it requires tidal disruption that is suppressed by
the more massive impactors.
