Building massive compact planetesimal disks from the accretion of pebbles

TL;DR

This paper proposes a model where planetesimal disks grow rapidly from pebble accretion, naturally forming massive, compact disks in most systems without special conditions, influencing planetary system formation theories.

Contribution

The model demonstrates that pebble accretion onto existing planetesimals can produce massive disks without requiring enhanced formation conditions or massive initial disks.

Findings

Inner disk accretes pebbles faster than direct planetesimal formation.

High mass planetesimal disks form naturally in most systems.

Disk mass correlates with pebble flux and stellar properties.

Abstract

We present a model in which planetesimal disks are built from the combination of planetesimal formation and accretion of radially drifting pebbles onto existing planetesimals. In this model, the rate of accretion of pebbles onto planetesimals quickly outpaces the rate of direct planetesimal formation in the inner disk. This allows for the formation of a high mass inner disk without the need for enhanced planetesimal formation or a massive protoplanetary disk. Our proposed mechanism for planetesimal disk growth does not require any special conditions to operate. Consequently, we expect that high mass planetesimal disks form naturally in nearly all systems. The extent of this growth is controlled by the total mass in pebbles that drifts through the inner disk. Anything that reduces the rate or duration of pebble delivery will correspondingly reduce the final mass of the planetesimal disk. Therefore, we expect that low mass stars (with less massive protoplanetary disks), low metallicity stars and stars with giant planets should all grow less massive planetesimal disks. The evolution of planetesimal disks into planetary systems remains a mystery. However, we argue that late stage planet formation models should begin with a massive disk. This reinforces the idea that massive and compact planetary systems could form in situ but does not exclude the possibility that significant migration occurs post-planet formation.