Embryo impacts and gas giant mergers I: Dichotomy of Jupiter and Saturn's core mass

TL;DR

This paper explores how giant planet collisions and embryo impacts can explain the differences in core mass and structure between Jupiter and Saturn, using numerical simulations to demonstrate core growth and erosion processes.

Contribution

It introduces a model where embryo impacts and giant mergers account for the structural diversity of gas giants, supported by numerical simulations of impact outcomes.

Findings

Embryo impacts can deposit heavy elements outside cores, promoting core growth.

Giant collisions can lead to core erosion and envelope mixing.

Impact energy influences core mass and planetary structure diversity.

Abstract

Interior to the gaseous envelopes of Saturn, Uranus, and Neptune, there are high-density cores with masses larger than 10 Earth masses. According to the conventional sequential accretion hypothesis, such massive cores are needed for the onset of efficient accretion of their gaseous envelopes. However, Jupiter's gaseous envelope is more massive and core may be less massive than those of Saturn. In order to account for this structural diversity and the super-solar metallicity in the envelope of Jupiter and Saturn, we investigate the possibility that they may have either merged with other gas giants or consumed several Earth-mass proto-planetary embryos during or after the rapid accretion of their envelope. In general, impinging sub-Earth-mass planetesimals disintegrate in gas giants' envelopes deposit heavy elements well outside the cores and locally suppress the convection. Consequently, their fragments sediment to promote the growth of cores. Through a series of numerical simulations, we show that it is possible for colliding super-Earth-mass embryos to reach the cores of gas giants. Direct parabolic collisions also lead to the coalescence of gas giants and merging of their cores. In these cases, the energy released from the impact leads to vigorous convective motion throughout the envelope and the erosion of the cores. This dichotomy contributes to the observed dispersion in the internal structure and atmospheric composition between Jupiter and Saturn and other gas giant planets and elsewhere.