Could Uranus and Neptune form by collisions of planetary embryos?

Abstract:

The origin of Uranus and Neptune remains a challenge for formation models of the solar system. A potential explanation is that the planets formed from a population of a few planetary embryos with masses of a few Earth masses which formed beyond Saturn's orbit and migrated inwards. These embryos can collide and merge to form Uranus and Neptune.
In this work we revisit this formation scenario and investigate the outcomes of such collisions using 3D hydrodynamical simulations. We hence connect impact simulations to formation models by taking the initial conditions from the n-body simulations. We investigate under what conditions the perfect-merging assumption is appropriate, and infer the planets’ final masses, obliquities and rotation periods, and the presence of proto-satellite disks.
Finally, we identify the formation paths that lead to planets that are consistent with the basic physical properties of Uranus and Neptune.