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

TL;DR

This paper proposes a collisional tilting scenario for Uranus that explains the prograde equatorial orbits of its satellites despite the planet's large obliquity, involving a temporary ring and disk precession.

Contribution

It introduces a new collisional tilting model that accounts for the formation of Uranus's equatorial prograde satellites in the context of its obliquity history.

Findings

Proposes a collisional tilting mechanism involving a temporary ring.

Explains the formation of a thin equatorial satellite disk.

Suggests Uranus had a significant initial obliquity before tilting to 98°.

Abstract

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.