On the origin of wide-orbit ALMA planets: giant protoplanets disrupted by their cores

TL;DR

This study uses 3D simulations to show that giant protoplanets can be disrupted by growing solid cores, potentially explaining the presence of wide-orbit sub-Jovian planets observed in young protoplanetary discs.

Contribution

First 3D global disc simulations demonstrating that massive GI protoplanets can self-destruct due to core growth, explaining wide-orbit sub-Jovian planets.

Findings

Giant protoplanets can be disrupted at large distances if cores grow inside them.

Heating force perturbs cores, leading to complex dust and core dynamics.

Predicts sub-Jovian planets at wide orbits in early discs.

Abstract

Recent ALMA observations may indicate a surprising abundance of sub-Jovian planets on very wide orbits in protoplanetary discs that are only a few million years old. These planets are too young and distant to have been formed via the Core Accretion (CA) scenario, and are much less massive than the gas clumps born in the classical Gravitational Instability (GI) theory. It was recently suggested that such planets may form by the partial destruction of GI protoplanets: energy output due to the growth of a massive core may unbind all or most of the surrounding pre-collapse protoplanet. Here we present the first 3D global disc simulations that simultaneously resolve grain dynamics in the disc and within the protoplanet. We confirm that massive GI protoplanets may self-destruct at arbitrarily large separations from the host star provided that solid cores of mass around 10-20 Earth masses are able to grow inside them during their pre-collapse phase. In addition, we find that the heating force recently analysed by Masset and Velasco Romero (2017) perturbs these cores away from the centre of their gaseous protoplanets. This leads to very complicated dust dynamics in the protoplanet centre, potentially resulting in the formation of multiple cores, planetary satellites, and other debris such as planetesimals within the same protoplanet. A unique prediction of this planet formation scenario is the presence of sub-Jovian planets at wide orbits in Class 0/I protoplanetary discs.