Measuring the Collisional Evolution of Debris Clusters in an Asteroid System

TL;DR

This study uses advanced simulations to investigate how debris clouds around rotating asteroids evolve dynamically and collide, leading to the formation of larger, structured clusters that could be precursors to binary asteroid systems.

Contribution

It introduces a novel simulation framework combining full-scale and cluster-scale models to efficiently study collisional growth in asteroid debris clouds.

Findings

Debris particles migrate to low-potential regions, shaping the cloud structure.

Collisional velocities follow a Weibull distribution, favoring accretion.

Clusters grow from centimeters to meters, forming porous, compact structures.

Abstract

Context. Rotational instability of rubble-pile asteroids can trigger mass shedding, forming transient debris clouds that may provide the initial conditions for secondary formation in binary systems. Aims. We investigate the dynamical and collisional evolution of a debris cloud numerically generated around a Didymos-like progenitor, as a representative case for the early formation of Dimorphos. The analysis focuses on the growth and structural properties of clusters composed of centimetre- to decimetre-scale particles. Methods. We perform full-scale simulations of debris evolution around a near-critically rotating asteroid using a cross-spatial-scale approach combined with the discrete element method (DEM). To overcome computational timescale limitations, an equivalent cluster-scale simulation framework is introduced to capture the essential collisional growth processes efficiently. These simulations quantify the efficiency of cluster growth and the structural evoution within the debris cloud. Results. Our simulations reveal that particles shed from a rotationally unstable asteroid exhibit a consistent migration pattern toward low-geopotential regions, which governs the mass distribution and dynamical structure of the debris cloud. The collisional velocity are well described by a Weibull distribution (lambda = 0.0642, k = 1.8349), where low-velocity impacts favor accretion. These collisions enable clusters to grow from centimeter-decimeter scales to meter-sized bodies, developing compact, moderately porous structures (Delta I \approx 0.8, phi \approx 0.52). Collisions between meter-sized clusters do not exhibit a bouncing barrier: low-velocity impacts yield Dinkinesh-like shapes, while moderate velocities promote plastic merging and continued growth.