Can the Uranian Satellites Form from a Debris Disk Generated by a Giant Impact?

TL;DR

This study investigates whether Uranian satellites could have formed from a debris disk generated by a giant impact, using N-body simulations, and suggests that in-situ formation from the initial disk is unlikely without considering subsequent disk evolution.

Contribution

The paper demonstrates that the initial debris disk alone cannot reproduce the current satellite distribution, highlighting the importance of thermal and viscous evolution in satellite formation.

Findings

Initial debris disk models fail to match satellite masses and positions.

Orbital evolution due to planetary tides influences satellite formation.

In-situ formation requires considering disk evolution post-impact.

Abstract

Hydrodynamic simulations of a giant impact to proto-Uranus indicated that such an impact could tilt its rotational axis and produce a circumplanetary debris disk beyond the corotation radius of Uranus. However, whether Uranian satellites can actually be formed from such a wide disk remains unclear. Herein, we modeled a wide debris disk of solids with several initial conditions inferred from the hydrodynamic simulations, and performed $N$-body simulations to investigate in-situ satellite formation from the debris disk. We also took account of orbital evolutions of satellites due to the planetary tides after the growth of satellites. We found that, in any case, the orbital distribution of the five major satellites could not be reproduced from the disk as long as the power index of its surface density is similar to that of the disk generated just after the giant impact: Satellites in the middle region obtained much larger masses than Ariel or Umbriel, while the outermost satellite did not grow to the mass of Oberon. Our results indicate that we should consider the thermal and viscous evolution of the evaporated disk after the giant impact to form the five major satellites through the in-situ formation scenario. On the other hand, the small inner satellites would be formed from the rings produced by the disrupted satellites which migrated from around the corotation radius of Uranus due to the planetary tides.