On the formation of compact planetary systems via concurrent core accretion and migration

TL;DR

This study uses comprehensive N-body simulations to explore how planetary systems similar to observed compact low-mass multi-planet systems can form through concurrent core accretion and migration, emphasizing the role of small, mobile bodies.

Contribution

It demonstrates that specific initial conditions and small body mobility are crucial for forming compact planetary systems akin to those observed.

Findings

Compact systems with terrestrial planets, super-Earths, and Neptunes naturally emerge under certain parameters.

Low solids-to-gas ratio discs can produce short-period super-Earths if small bodies dominate accretion.

Presence of short-period super-Earths around low metallicity stars suggests small, mobile bodies are key in planet formation.

Abstract

We present the results of planet formation N-body simulations based on a comprehensive physical model that includes planetary mass growth through mutual embryo collisions and planetesimal/boulder accretion, viscous disc evolution, planetary migration and gas accretion onto planetary cores. The main aim of this study is to determine which set of model parameters leads to the formation of planetary systems that are similar to the compact low mass multi-planet systems that have been discovered by radial velocity surveys and the Kepler mission. We vary the initial disc mass, solids-to-gas ratio and the sizes of the boulders/planetesimals, and for a restricted volume of the parameter space we find that compact systems containing terrestrial planets, super-Earths and Neptune-like bodies arise as natural outcomes of the simulations. Disc models with low values of the solids-to-gas ratio can only form short-period super-Earths and Neptunes when small planetesimals/boulders provide the main source of accretion, since the mobility of these bodies is required to overcome the local isolation masses for growing embryos. The existence of short-period super-Earths around low metallicity stars provides strong evidence that small, mobile bodies (planetesimals, boulders or pebbles) played a central role in the formation of the observed planets.