The shape distribution of asteroid families -- evidence for evolution driven by small impacts

TL;DR

This study analyzes asteroid brightness variability to understand how their shapes evolve from elongated to spheroidal forms due to impact processes, revealing insights into asteroid family ages and structural composition.

Contribution

It provides the first large-scale statistical analysis of asteroid shape distribution across families, demonstrating impact-driven shape evolution and identifying impact-resistant cores.

Findings

Young asteroid families have diverse elongations indicating recent fragmentation.

Older families show more spheroidal shapes consistent with impact erosion.

A small percentage of asteroids are very elongated, likely young fragments or reshaped bodies.

Abstract

A statistical analysis of brightness variability of asteroids reveals how their shapes evolve from elongated to rough spheroidal forms, presumably driven by impact-related phenomena. Based on the Sloan Digital Sky Survey Moving Object Catalog, we determined the shape distribution of 11,735 asteroids, with special emphasis on eight prominent asteroid families. In young families, asteroids have a wide range of shape elongations, implying fragmentation-formation. In older families we see an increasing number of rough spheroids, in agreement with the predictions of an impact-driven evolution. Old families also contain a group of moderately elongated members, which we suggest correspond to higher-density, more impact-resistant cores of former fragmented asteroids that have undergone slow shape erosion. A few percent of asteroids have very elongated shapes, and can either be young fragments or tidally reshaped bodies. Our results confirm that the majority of asteroids are gravitationally bound ``rubble piles''.