Formation of Giant Planet Satellites

Abstract

Recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of a 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 • ∼0.1-10 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 subdisk into 100 km satellitesimals. Subsequently, satellite conglomeration ensues via pair-wise 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 photoevaporation 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.

As the Worlds Turn: Constraining Spin Evolution in the Planetary-mass Regime

“…More specifically, at ages 10 Myr, PMOs spin at rates 5%-20% of break-up, consistent with their rotation having been regulated by magnetic torques exerted by circum-PMO disks (CPDs). We speculate that such CPDs could be the breeding grounds for satellite systems like the Galilean moons (Canup & Ward 2002Batygin & Morbidelli 2020).…”

Contemporary formation of early Solar System planetesimals at two distinct radial locations

“…Here, by modeling the evolution of a disk with ongoing accretion of material from the collapsing molecular cloud [17][18][19] , we show that planetesimal formation may have been triggered within the first 0.5 million years by dust pile-up at both the snowline (at ~5 au) and the silicate sublimation line (at ~1 au), provided turbulent diffusion was low. Particle concentration at ~1 au is due to the early outward radial motion of gas [20] and is assisted by the sublimation and recondensation of silicates [21,22] . Our results indicate that, although the planetesimals at the two locations formed about contemporaneously, those at the snowline accreted a large fraction of their mass (~60%) from materials delivered to the disk in the first few 10 4 yr, whereas this fraction is only 30% for the planetesimals formed at the silicate line.…”

“…directed away from the star) beyond the centrifugal radius, whereas, when the inflow wanes, the disk rapidly becomes an accretion disk with a negative radial velocity in its inner part. Because a positive radial velocity of the gas can help in trapping dust particles [20] we look for disks that have a protracted phase of radial expansion in their inner part. Assuming a centrifugal radius decreasing as Rc=0.35au/(Msun(t)) 0.5 , we obtain a disk that expands radially beyond 0.4 au during the first 0.3 Myr (Fig.…”

The Fundamental Connections between the Solar System and Exoplanetary Science

“…Given the prevalence of satellites within the Solar System, substantial effort is being devoted to the search for moons orbiting exoplanets (e.g., Heller et al., 2014; Hill et al., 2018; Hinkel & Kane, 2013; Kipping et al., 2013). Furthermore, formation of regular moons, such as those in the Galilean system, may serve as analogs of compact exoplanetary systems in terms of their formation and architectures (Batygin & Morbidelli, 2020; Dobos et al., 2019; Kane, Hinkel, et al., 2013; Makarov et al., 2018). However, there are numerous questions that remain regarding the wide array of moons in the Solar System, including their geology and, in some cases, atmospheres.…”