Toward a Deterministic Model of Planetary Formation VI: Dynamical Interaction and Coagulation of Multiple Rocky Embryos and Super-Earth Systems around Solar Type Stars

TL;DR

This paper presents a modified numerical model demonstrating how multiple rocky embryos can form, migrate, and assemble into super-Earth systems close to their host stars through dynamical interactions and collisions.

Contribution

It introduces a new simulation approach that accounts for embryo-disk interactions and mutual scattering, explaining the formation of compact super-Earth systems.

Findings

Super-Earths can form interior to the ice line and migrate inward.

Close scattering and giant impacts lead to non-resonant, compact super-Earth systems.

Most refractory super-Earths with short periods likely formed through this process.

Abstract

Radial velocity and transit surveys indicate that solar-type stars bear super-Earths, with mass and period up to ~ 20 M_E and a few months, are more common than those with Jupiter-mass gas giants. In many cases, these super-Earths are members of multiple-planet systems in which their mutual dynamical interaction has influenced their formation and evolution. In this paper, we modify an existing numerical population synthesis scheme to take into account protoplanetary embryos' interaction with their evolving natal gaseous disk, as well as their close scatterings and resonant interaction with each other. We show that it is possible for a group of compact embryos to emerge interior to the ice line, grow, migrate, and congregate into closely-packed convoys which stall in the proximity of their host stars. After the disk-gas depletion, they undergo orbit crossing, close scattering, and giant impacts to form multiple rocky Earths or super-Earths in non-resonant orbits around ~ 0.1AU with moderate eccentricities of ~0.01-0.1. We suggest that most refractory super-Earths with period in the range of a few days to weeks may have formed through this process. These super-Earths differ from Neptune-like ice giants by their compact sizes and lack of a substantial gaseous envelope.