Abstract

Contributed Talk - Splinter MinorBodies

Tuesday, 10 September 2024, 14:35   (S21)

The formation of the Galilean moons and Titan in the Grand Tack scenario

René Heller, Gabriel D. Marleau, Ralph Pudritz
Max Planck Institute for Solar System Science, Universität Duisburg-Essen, McMaster University

In the Grand Tack (GT) scenario for the young solar system, Jupiter formed beyond 3.5 AU from the Sun and migrated as close as 1.5 AU until it encountered an orbital resonance with Saturn. Both planets then supposedly migrated outward for several hundred thousands years, with Jupiter ending up near 5 AU. Here we explore the timing between Jupiter's migration and the formation of the Galilean satellites. We study the formation of Ganymede and Callisto, both of which consist of about 50% water and rock, in the GT scenario. We examine why they lack dense atmospheres, while Titan is surrounded by a thick nitrogen gas envelope. We model an axially symmetric circumplanetary disk (CPD) in hydrostatic equilibrium around Jupiter. The CPD is warmed by viscous heating, Jupiter's luminosity, accretional heating, and solar radiation. The position of the water ice line in the CPD, which is crucial for the formation of massive moons, is computed at various solar distances. We assess the loss of Galilean atmospheres due to high-energy radiation from the young Sun. Ganymede and Callisto cannot have accreted their water during Jupiter's supposed GT, because its CPD (if still active) was too warm to host ices and much smaller than Ganymede's contemporary orbit. From a thermal perspective, the Galilean moons might have had significant atmospheres, but these would probably have been eroded during the GT in less than a hundred thousand years by solar XUV radiation. Jupiter and the Galilean moons formed beyond 4.5 (+/- 0.5 AU) and prior to the proposed GT. Thereafter, Jupiter's CPD would have been dry, and delayed accretion of planetesimals should have created water-rich Io and Europa. While Galilean atmospheres would have been lost during the GT, Titan would have formed after Saturn's own tack, because Saturn still accreted substantially for about a millions years after its closest solar approach.