Rotation-Dependent Catastrophic Disruption of Gravitational Aggregates

TL;DR

This study investigates how pre-impact rotation affects collision outcomes of planetesimals, revealing that rotation generally lowers the energy needed for catastrophic disruption and developing models to quantify this effect.

Contribution

It introduces a systematic analysis of rotation effects on collision thresholds using advanced simulations and develops a semi-analytic model consistent with existing disruption laws.

Findings

Rotation lowers the catastrophic disruption threshold energy.

A semi-analytic model describes the impact of rotation on collision outcomes.

Re-scaled variables account for impact angles and rotation, enabling comparison across scenarios.

Abstract

We carry out a systematic exploration of the effect of pre-impact rotation on the outcomes of low-speed collisions between planetesimals modeled as gravitational aggregates. We use pkdgrav, a cosmology code adapted to collisional problems and recently enhanced with a new soft-sphere collision algorithm that includes more realistic contact forces. A rotating body has lower effective surface gravity than a non-rotating one and therefore might suffer more mass loss as the result of a collision. What is less well understood, however, is whether rotation systematically increases mass loss on average regardless of the impact trajectory. This has important implications for the efficiency of planet formation via planetesimal growth, and also more generally for the determination of the impact energy threshold for catastrophic disruption (leading to the largest remnant retaining 50% of the original mass), as this has generally only been evaluated for non-spinning bodies. We find that for most collision scenarios, rotation lowers the threshold energy for catastrophic dispersal. For head-on collisions, we develop a semi-analytic description of the change in the threshold description as a function of the target's pre-impact rotation rate, and find that these results are consistent with the "universal law" of catastrophic disruption developed by Leinhardt & Stewart. Using this approach, we introduce re-scaled catastrophic disruption variables that take into account the interacting mass fraction of the target and the projectile in order to translate oblique impacts into equivalent head-on collisions.