Deciphering the Origin of the Regular Satellites of Gaseous Giants - Iapetus: the Rosetta Ice-Moon

TL;DR

This paper proposes a model explaining the formation and composition of Iapetus and other regular satellites of gaseous giants through accretion from collisional debris in a two-component gaseous subnebula, accounting for observed compositional differences.

Contribution

It introduces a new formation model for regular satellites based on collisional debris accretion in a two-component subnebula, explaining compositional variations.

Findings

Iapetus's composition can be explained by accretion from collisional debris.

The model accounts for the ice enrichment in Iapetus and other satellites.

It provides a natural explanation for compositional differences in satellite populations.

Abstract

Here we show that Iapetus can serve to discriminate between satellite formation models. Its accretion history can be understood in terms of a two-component gaseous subnebula, with a relatively dense inner region, and an extended tail out to the location of the irregular satellites, as in the SEMM model of Mosqueira and Estrada (2003a,b). Following giant planet formation, planetesimals in the feeding zone of Jupiter and Saturn become dynamically excited, and undergo a collisional cascade. Ablation and capture of planetesimal fragments crossing the gaseous circumplanetary disks delivers enough collisional rubble to account for the mass budgets of the regular satellites of Jupiter and Saturn. This process can result in rock/ice fractionation provided the make up of the population of disk crossers is non-homogeneous, thus offering a natural explanation for the marked compositional differences between outer solar nebula objects and those that accreted in the subnebulae of the giant planets. Consequently, our model leads to an enhancement of the ice content of Iapetus, and to a lesser degree those of Ganymede, Titan and Callisto, and accounts for the (non-stochastic) compositions of these large, low-porosity outer regular satellites of Jupiter and Saturn. (abridged)