Standing on the shoulders of giants: Trojan Earths and vortex trapping in low mass self-gravitating protoplanetary disks of gas and solids

TL;DR

This study demonstrates that in low-mass, self-gravitating protoplanetary disks, solid particles can rapidly collapse into planetary bodies within stable regions near giant planets, leading to diverse planet formation scenarios.

Contribution

It provides detailed simulations showing how particles of different sizes collapse into planets at Lagrangian points and vortex edges, revealing new pathways for planet formation in protoplanetary disks.

Findings

1 cm particles collapse into Earth-mass planets in less than 200 orbits.

Vortices can trap 30 cm particles, forming Super-Earths up to 17 Earth masses.

Multiple particle sizes lead to shifted stable points and varied planet masses.

Abstract

Centimeter and meter sized solid particles in protoplanetary disks are trapped within long lived high pressure regions, creating opportunities for collapse into planetesimals and planetary embryos. We study the accumulations in the stable Lagrangian points of a giant planet, as well as in the Rossby vortices launched at the edges of the gap it carves. We employ the Pencil Code, tracing the solids with a large number of interacting Lagrangian particles, usually 100,000. For particles of 1 cm to 10 cm radii, gravitational collapse occurs in the Lagrangian points in less than 200 orbits. For 5 cm particles, a 2 Earth mass planet is formed. For 10 cm, the final maximum collapsed mass is around 3 Earth masses. The collapse of the 1 cm particles is indirect, following the timescale of depletion of gas from the tadpole orbits. In the edges of the gap vortices are excited, trapping preferentially particles of 30 cm radii. The rocky planet that is formed is as massive as 17 Earth masses, constituting a Super-Earth. By using multiple particle species, we find that gas drag modifies the streamlines in the tadpole region around the classical L4 and L5 points. As a result, particles of different radii have their stable points shifted to different locations. Collapse therefore takes longer and produces planets of lower mass. Three super-Earths are formed in the vortices, the most massive having 4.4 Earth masses. We conclude that a Jupiter mass planet can induce the formation of other planetary embryos in the outer edge of its gas gap. Trojan Earth mass planets are readily formed, and although not existing in the solar system, might be common in the exoplanetary zoo.