The physics of protoplanetesimal dust agglomerates. VII The low-velocity collision behavior of large dust agglomerates

TL;DR

This study investigates how large dust agglomerates behave during low-velocity collisions in microgravity, revealing a transition from solid-like to granular behavior and providing new insights relevant to planetary formation.

Contribution

It extends previous experiments to larger dust aggregates, providing detailed measurements of collision outcomes and a theoretical interpretation of the velocity-dependent restitution behavior.

Findings

Coefficient of restitution decreases with velocity at low speeds.

At higher velocities, restitution becomes constant before fragmentation.

Molecular dynamics simulations match experimental data reasonably well.

Abstract

We performed micro-gravity collision experiments in our laboratory drop-tower using 5-cm-sized dust agglomerates with volume filling factors of 0.3 and 0.4, respectively. This work is an extension of our previous experiments reported in Beitz et al. (2011) to aggregates of more than one order of magnitude higher masses. The dust aggregates consisted of micrometer-sized silica particles and were macroscopically homogeneous. We measured the coefficient of restitution for collision velocities ranging from 1 cm/s to 0.5 m/s, and determined the fragmentation velocity. For low velocities, the coefficient of restitution decreases with increasing impact velocity, in contrast to findings by Beitz et al. (2011). At higher velocities, the value of the coefficient of restitution becomes constant, before the aggregates break at the onset of fragmentation. We interpret the qualitative change in the coefficient of restitution as the transition from a solid-body-dominated to a granular-medium-dominated behavior. We complement our experiments by molecular dynamics simulations of porous aggregates and obtain a reasonable match to the experimental data. We discuss the importance of our experiments for protoplanetary disks, debris disks, and planetary rings. The work is an extensional study to previous work of our group and gives a new insight in the velocity dependency of the coefficient of restitution due to improved measurements, better statistics and a theoretical approach.