Formation of Giant Planet Satellites

TL;DR

This paper proposes a new model for the formation of giant planet satellites, emphasizing the role of circumplanetary disks as dust traps and the gravitational fragmentation process, aligning well with observed moon systems.

Contribution

It introduces a novel formation scenario involving dust trapping, metallicity increase, and fragmentation, supported by numerical simulations matching observed satellite properties.

Findings

Circumplanetary disks act as dust traps for mm-sized grains.

Satellite-sized objects form via gravitational fragmentation in the solid disk.

Model results agree with the properties of Jupiter's and Saturn's moons.

Abstract

Recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of large-scale meridional flow of gas inside the planetary Hill sphere. This circulation feeds a circumplanetary disk that viscously expels gaseous material back into the parent nebula, maintaining the system in a quasi-steady state. Here we investigate the formation of natural satellites of Jupiter and Saturn within the framework of this newly outlined picture. We begin by considering the long-term evolution of solid material, and demonstrate that the circumplanetary disk can act as a global dust trap, where $s_{\bullet}\sim0.1-10\,$mm grains achieve a hydrodynamical equilibrium, facilitated by a balance between radial updraft and aerodynamic drag. This process leads to a gradual increase in the system's metallicity, and eventually culminates in the gravitational fragmentation of the outer regions of the solid sub-disk into $\mathcal{R}\sim100\,$km satellitesimals. Subsequently, satellite conglomeration ensues via pairwise collisions, but is terminated when disk-driven orbital migration removes the growing objects from the satellitesimal feeding zone. The resulting satellite formation cycle can repeat multiple times, until it is brought to an end by photo-evaporation of the parent nebula. Numerical simulations of the envisioned formation scenario yield satisfactory agreement between our model and the known properties of the Jovian and Saturnian moons.