Particle Clumping and Planetesimal Formation Depend Strongly on Metallicity

TL;DR

This study uses 3D simulations to show that higher metallicity in protoplanetary disks significantly enhances particle clumping, facilitating planetesimal formation, and suggests a link between stellar metallicity and planet formation.

Contribution

It demonstrates how varying metallicity affects particle clumping and planetesimal formation, highlighting the importance of metallicity in early planet formation processes.

Findings

Clumping is weak at solar metallicity levels.

Doubling metallicity leads to strong clumping and high-density particle regions.

Gravitational collapse of clumps forms 100 km planetesimals.

Abstract

We present three-dimensional numerical simulations of particle clumping and planetesimal formation in protoplanetary disks with varying amounts of solid material. As centimeter-size pebbles settle to the mid-plane, turbulence develops through vertical shearing and streaming instabilities. We find that when the pebble-to-gas column density ratio is 0.01, corresponding roughly to solar metallicity, clumping is weak, so the pebble density rarely exceeds the gas density. Doubling the column density ratio leads to a dramatic increase in clumping, with characteristic particle densities more than ten times the gas density and maximum densities reaching several thousand times the gas density. This is consistent with unstratified simulations of the streaming instability that show strong clumping in particle dominated flows. The clumps readily contract gravitationally into interacting planetesimals of order 100 km in radius. Our results suggest that the correlation between host star metallicity and exoplanets may reflect the early stages of planet formation. We further speculate that initially low metallicity disks can be particle enriched during the gas dispersal phase, leading to a late burst of planetesimal formation.