Early formation of moons around large trans-Neptunian objects via giant impacts

TL;DR

This study uses hydrodynamic simulations to demonstrate that giant impacts can explain the formation and current properties of satellite systems around large trans-Neptunian objects, supporting a common origin in early solar system history.

Contribution

The paper provides the first systematic simulation-based evidence that giant impacts can produce the observed satellite characteristics of large TNOs, including mass ratios and orbital properties.

Findings

Simulated mass ratios match observed ranges.

Satellite spin and orbital evolution explain current distributions.

Impacts occurred before Neptune's migration, involving molten bodies.

Abstract

Recent studies have revealed that all large (over 1000 km in diameter) trans-Neptunian objects (TNOs) form satellite systems. Although the largest Plutonian satellite, Charon, is thought to be an intact fragment of an impactor directly formed via a giant impact, whether giant impacts can explain the variations in secondary-to-primary mass ratios and spin/orbital periods among all large TNOs remains to be determined. Here we systematically perform hydrodynamic simulations to investigate satellite formation via giant impacts. We find that the simulated secondary-to-primary mass ratio varies over a wide range, which overlaps with observed mass ratios. We also reveal that the satellite systems' current distribution of spin/orbital periods and small eccentricity can be explained only when their spins and orbits tidally evolve: initially as fluid-like bodies, but finally as rigid bodies. These results suggest that all satellites of large TNOs were formed via giant impacts in the early stage of solar system formation, before the outward migration of Neptune, and that they were fully or partially molten during the giant impact era.