The Physics of Protoplanetesimal Dust Agglomerates. Vi. Erosion of Large Aggregates as a Source of Micrometer-Sized Particles

TL;DR

This paper investigates how erosion of large dust agglomerates by micrometer-sized particles in protoplanetary disks contributes significantly to the abundance of small particles, combining experiments, modeling, and observational data analysis.

Contribution

It provides experimental evidence and a numerical model showing erosion halts at certain velocities, and develops an analytical disk model demonstrating erosion as a key source of micrometer-sized particles.

Findings

Erosion halts at impact velocities up to ~30 m/s due to surface compression.

Erosion rate decreases by an order of magnitude at higher velocities.

The model explains the observed abundance of micrometer-sized particles in disks.

Abstract

Observed protoplanetary disks consist of a large amount of micrometer-sized particles. Dullemond and Dominik (2005) pointed out for the first time the difficulty in explaining the strong mid-IR excess of classical T-Tauri stars without any dust-retention mechanisms. Because high relative velocities in between micrometer-sized and macroscopic particles exist in protoplanetary disks, we present experimental results on the erosion of macroscopic agglomerates consisting of micrometer-sized spherical particles via the impact of micrometer-sized particles. We find that after an initial phase, in which an impacting particle erodes up to 10 particles of an agglomerate, the impacting particles compress the agglomerate's surface, which partly passivates the agglomerates against erosion. Due to this effect the erosion halts within our error bars for impact velocities up to ~30 m/s. For larger velocities, the erosion is reduced by an order of magnitude. This outcome is explained and confirmed by a numerical model. In a next step we build an analytical disk model and implement the experimentally found erosive effect. The model shows that erosion is a strong source of micrometer-sized particles in a protoplanetary disk. Finally we use the stationary solution of this model to explain the amount of micrometer-sized particles in observational infrared data of Furlan et al. (2006).