The growth of super-large pre-planetary pebbles to an impact erosion limit

TL;DR

This study identifies a velocity threshold for impact erosion of pebbles in protoplanetary disks, suggesting the formation of larger pebbles that could aid planetesimal development.

Contribution

It provides experimental and simulation evidence for an impact erosion limit, advancing understanding of particle growth beyond the bouncing barrier in planet formation.

Findings

Impact erosion threshold velocity is about 0.5 m/s.

Pebbles can grow to several centimeters in size.

Hydrodynamic interactions may facilitate planetesimal formation.

Abstract

Early dust evolution in protoplanetary disks is dominated by sticking collisions. However, this initial phase of particle growth faces constraints - notably from destructive encounters. To find the maximum particle size achievable, we studied collisional processes during a prolonged microgravity experiment aboard a suborbital flight. Here, we specifically report an impact erosion limit. We observed individual basalt beads, each measuring 0.5 mm in diameter, colliding with and either eroding or adhering to a cluster several centimeters in size. This cluster, formed from tribocharged particles, simulates an electrostatic growth phase that surpasses the classical bouncing barrier. We find a threshold velocity of about 0.5 m/s, distinguishing between additive and erosive impacts of individual beads. Numerical simulations of grain impacts into clusters, testing both low and high charge constituents corroborate the experimental findings of surface erosion within the observed velocity range. This specific velocity threshold suggests the potential formation of pebbles several centimeters in size within protoplanetary disks. Such dimensions place these pebbles well into a regime where hydrodynamic interaction might facilitate the formation of planetesimals.