The Physics of Protoplanetesimal Dust Agglomerates II. Low Velocity Collision Properties

TL;DR

This study investigates low-velocity collisions of high-porosity dust aggregates in microgravity, revealing conditions for sticking, bouncing, and mass transfer, which are crucial for understanding early planet formation.

Contribution

It provides new experimental data on collision outcomes of porous dust aggregates, highlighting the effects of porosity, impact angle, and surface curvature on sticking and bouncing behaviors.

Findings

High-porosity targets mostly lead to sticking at low velocities.

Less porous aggregates tend to bounce with some mass transfer.

Impact outcomes depend on porosity, impact angle, and surface curvature.

Abstract

For the investigation of collisions among protoplanetesimal dust aggregates, we performed microgravity experiments in which the impacts of high-porosity mm-sized dust aggregates into 2.5 cm-sized high-porosity dust aggregates can be studied. The dust aggregates consisted of micrometer-sized dust grains and were produced by random ballistic deposition with porosities between 85% and 93%. Impact velocities ranged from ~0.1 m/s to ~3 m/s and impact angles were almost randomly distributed. We also used "molded" target aggregates such that the radii of the local surface curvatures corresponded to the projectile radii. The experiments showed that impacts into the highest-porosity targets almost always led to sticking, whereas for the less porous dust aggregates, the collisions with intermediate velocities and high impact angles resulted in the bouncing of the projectile with a mass transfer from the target to the projectile aggregate. Sticking probabilities for the impacts into the "molded" target aggregates were considerably decreased. For the impacts into smooth targets, we measured the depth of intrusion and the crater volume and could derive some interesting dynamical properties which can help to derive a collision model for protoplanetesimal dust aggregates. Future models of the aggregate growth in protoplanetary disks should take into account non-central impacts, impact compression, the influence of the local radius of curvature on the collisional outcome and the possible mass transfer between target and projectile agglomerates in non-sticking collisions.