Origin of the Different Architectures of the Jovian and Saturnian Satellite Systems

TL;DR

This study investigates the origins of the contrasting architectures of Jovian and Saturnian satellite systems through semi-analytical simulations, revealing how disk evolution and migration processes lead to their distinct satellite configurations.

Contribution

The paper introduces new models of disk evolution and migration that explain the formation differences between Jovian and Saturnian satellite systems, including the impact of gas infall termination and disk cavity evolution.

Findings

Jovian satellites likely form in resonant chains due to rapid migration and disk truncation.

Saturnian satellites tend to form a single dominant body due to slower gas infall decay.

Predicted satellite system properties align with observed mass and composition distributions.

Abstract

The Jovian regular satellite system mainly consists of four Galilean satellites that have similar masses and are trapped in mutual mean motion resonances except for the outer satellite, Callisto. On the other hand, the Saturnian regular satellite system has only one big icy body, Titan, and a population of much smaller icy moons. We have investigated the origin of these major differences between the Jovian and Saturnian satellite systems by semi-analytically simulating the growth and orbital migration of proto-satellites in an accreting proto-satellite disk. We set up two different disk evolution/structure models that correspond to Jovian and Saturnian systems, by building upon previously developed models of an actively-supplied proto-satellite disk, the formation of gas giants, and observations of young stars. Our simulations extend previous models by including the (1) different termination timescales of gas infall onto the proto-satellite disk and (2) different evolution of a cavity in the disk, between the Jovian and Saturnian systems. We have performed Monte Carlo simulations and show that in the case of the Jovian systems, four to five similar-mass satellites are likely to remain trapped in mean motion resonances. This orbital configuration is formed by type I migration, temporal stopping of the migration near the disk inner edge, and quick truncation of gas infall caused by Jupiter opening a gap in the Solar nebula. The Saturnian systems tend to end up with one dominant body in the outer regions caused by the slower decay of gas infall associated with global depletion of the Solar nebula. The total mass and compositional zoning of the predicted Jovian and Saturnian satellite systems are consistent with the observed satellite systems.