Erosion of planetesimals by gas flow

TL;DR

This paper investigates whether gas flow in protoplanetary disks can erode planetesimals, finding erosion possible mainly in the innermost disk regions and on short timescales for eccentric orbits.

Contribution

It provides a quantitative analysis of gas-induced erosion of planetesimals, combining shear stress estimates with numerical simulations to identify conditions leading to erosion.

Findings

Erosion occurs in the innermost disk regions for eccentric orbits.

Erosion timescales are short if erosion occurs.

Planetesimals outside 1 au are generally safe from erosion.

Abstract

The first stages of planet formation take place in protoplanetary disks that are largely made up of gas. Understanding how the gas affects planetesimals in the protoplanetary disk is therefore essential. In this paper, we discuss whether or not gas flow can erode planetesimals. We estimate how much shear stress is exerted onto the planetesimal surface by the gas as a function of disk and planetesimal properties. To determine whether erosion can take place, we compare this with previous measurements of the critical stress that a pebble-pile planetesimal can withstand before erosion begins. If erosion takes place, we estimate the erosion time of the affected planetesimals. We also illustrate our estimates with two-dimensional numerical simulations of flows around planetesimals using the lattice Boltzmann method. We find that the wall shear stress can overcome the critical stress of planetesimals in an eccentric orbit within the innermost regions of the disk. The high eccentricities needed to reach erosive stresses could be the result of shepherding by migrating planets. We also find that if a planetesimal erodes, it does so on short timescales. For planetesimals residing outside of $1 \ \rm{au}$, we find that they are mainly safe from erosion, even in the case of highly eccentric orbits.