Free Collisions in a Microgravity Many-Particle Experiment III: The Collision Behavior of sub-Millimeter-Sized Dust Aggregates

TL;DR

This study investigates collision outcomes of sub-millimeter dust aggregates in microgravity, revealing a velocity-dependent transition between sticking and bouncing, with implications for dust growth in space environments.

Contribution

The paper introduces an empirical power law for the collision threshold between sticking and bouncing, based on microgravity experiments, refining previous contact physics models.

Findings

Collision outcome depends mainly on impact velocity.

Transition between sticking and bouncing follows a shallower power law.

Dust aggregates can grow larger through aggregate-aggregate collisions.

Abstract

We conducted micro-gravity experiments to study the outcome of collisions between sub-mm-sized dust agglomerates consisting of \mu m-sized SiO2 monomer grains at velocities of several cm/s. Prior to the experiments, we used X-ray computer tomography (nano-CT) imaging to study the internal structure of these dust agglomerates and found no rim compaction so that their collision behavior is not governed by preparation-caused artefacts. We found that collisions between these dust aggregates can lead either to sticking or to bouncing, depending mostly on the impact velocity. While previous collision models derived the transition between both regimes from contact physics, we used the available empirical data from these and earlier experiments to derive a power law relation between dust-aggregate mass and impact velocity for the threshold between the two collision outcomes. In agreement with earlier experiments, we show that the transition between both regimes is not sharp, but follows a shallower power law than predicted by previous models (G\"uttler et al. 2010). Furthermore, we find that sticking between dust aggregates can lead to the formation of larger structures. Collisions between aggregates-of-aggregates can lead to growth at higher velocities than homogeneous dust agglomerates.