Formation of planets by tidal downsizing of giant planet embryos

TL;DR

This paper proposes a planet formation model where giant planet embryos form via disc fragmentation, migrate inward, and undergo tidal downsizing, leading to diverse planetary types including terrestrial planets and gas giants with solid cores.

Contribution

It introduces a comprehensive tidal downsizing model for planet formation, integrating disc fragmentation, core sedimentation, and tidal disruption processes.

Findings

Giant planet embryos form at large distances from the star.

Tidal downsizing can produce terrestrial planets and gas giants with cores.

The model explains the diversity of observed exoplanets.

Abstract

We hypothesise that planets are made by tidal downsizing of migrating giant planet embryos. The proposed scheme for planet formation consists of these steps: (i) a massive young protoplanetary disc fragments at R ~ several tens to hundreds of AU on gaseous clumps with masses of a few Jupiter masses; (ii) the clumps cool and contract, and simultaneously migrate closer in to the parent star; (iii) as earlier suggested by Boss (1998), dust sediments inside the gas clumps to form terrestrial mass solid cores; (iv) if the solid core becomes more massive than ~ 10 Earth masses, a massive gas atmosphere collapses onto the solid core; (v) when the gas clumps reach the inner few AU from the star, tidal shear and evaporation due to stellar irradiation peel off the outer metal-poor envelope of the clump. If tidal disruption occurs quickly, while the system is still in stage (iii), a terrestrial planet core is left. If it happens later, in stage (iv), a metal rich gas giant planet with a solid core emerges from the envelope.