Accretion of ice giant planets from massive protoplanets whose migration is blocked by Jupiter and Saturn

Abstract

ABSTRACT The growth and dynamical evolution of protoplanets beyond Saturn through collisions and type I migration typically result in a highly chaotic dynamics, producing a diversity of outcomes depending on the initial conditions. Here we present the results of N-bodies numerical simulations aiming to make a detailed exploration of different initial conditions and potential outcomes for this dynamics. We consider Jupiter and Saturn at the imminence of crossing the 3:2 mean motion resonance in two possible positions based on the final and initial conditions of the Grand Tack and the Nice models, respectively; four different gas disc lifetimes, and a range of population sizes of planetary embryos beyond Saturn with different masses and orbital configurations in a total of 72 different setups. We present statistical analyses of our outcomes including planets that ‘jump’ to interior orbits of Jupiter, the frequency of close encounters between the planetary embryos and Jupiter, the number of ejections and collisions, and the dynamical effects for stabilizing the final planetary system in chains of mean motion resonances. Results show that independently of the initial configuration of Jupiter and Saturn and the gas lifetime, the dynamical evolution goes through three main phases. A few per cent of the simulations successfully produce Uranus and Neptune analogues, which may have implications on the ice giants’ composition and obliquities, the material ejected from the Solar System, and the conditions for the giant planet instability.