Can the giant planets of the Solar System form via pebble accretion in a smooth protoplanetary disc?

¹ University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
e-mail: ch.lau@physik.uni-muenchen.de
² Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong
³ Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
⁴ Konkoly Observatory and Origins Research Institute, Research Centre for Astronomy and Earth Sciences, MTA Centre of Excellence, 15–17 Konkoly Thege Miklos ut, 1121 Budapest, Hungary
⁵ School of Science and Engineering, University of Dundee, Dundee DD1 4HN, UK

Received: 1 September 2023
Accepted: 8 January 2024

Abstract

Context. Prevailing N-body planet formation models typically start with lunar-mass embryos and show a general trend of rapid migration of massive planetary cores to the inner Solar System in the absence of a migration trap. This setup cannot capture the evolution from a planetesimal to embryo, which is crucial to the final architecture of the system.

Aims. We aim to model planet formation with planet migration starting with planetesimals of ~10⁻⁶−10⁻⁴ M_⊕ and reproduce the giant planets of the Solar System.

Methods. We simulated a population of 1000-5000 planetesimals in a smooth protoplanetary disc, which was evolved under the effects of their mutual gravity, pebble accretion, gas accretion, and planet migration, employing the parallelized N-body code SyMBAp.

Results. We find that the dynamical interactions among growing planetesimals are vigorous and can halt pebble accretion for excited bodies. While a set of results without planet migration produces one to two gas giants and one to two ice giants beyond 6 au, massive planetary cores readily move to the inner Solar System once planet migration is in effect.

Conclusions. Dynamical heating is important in a planetesimal disc and the reduced pebble encounter time should be considered in similar models. Planet migration remains a challenge to form cold giant planets in a smooth protoplanetary disc, which suggests an alternative mechanism is required to stop them at wide orbits.