Clumps in the Outer Disk by Disk Instability: Why They are Initially Gas Giants and the Legacy of Disruption

TL;DR

This paper investigates how gravitational instabilities in outer protoplanetary disks lead to initial formation of gas giant-like clumps, which can evolve into planetary cores or be disrupted, affecting planet formation and disk evolution.

Contribution

It combines analytic estimates with 3D simulations to show initial fragments are gas giant mass and discusses their evolution and potential disruption.

Findings

Initial fragments are in the gas giant mass range.

Clumps can survive multiple orbits before rapid collapse.

Disrupted clumps may lead to Earth-mass core formation.

Abstract

We explore the initial conditions for fragments in the extended regions ($r\gtrsim 50$ AU) of gravitationally unstable disks. We combine analytic estimates for the fragmentation of spiral arms with 3D SPH simulations to show that initial fragment masses are in the gas giant regime. These initial fragments will have substantial angular momentum, and should form disks with radii of a few AU. We show that clumps will survive for multiple orbits before they undergo a second, rapid collapse due to H$_2$ dissociation and that it is possible to destroy bound clumps by transporting them into the inner disk. The consequences of disrupted clumps for planet formation, dust processing, and disk evolution are discussed. We argue that it is possible to produce Earth-mass cores in the outer disk during the earliest phases of disk evolution.