Main Belt Asteroid Shape Distribution from Gaia DR2

TL;DR

This study analyzes Gaia DR2 data to estimate asteroid shapes, revealing size-dependent shape differences and correlations with other properties, thus advancing understanding of main belt asteroid morphology.

Contribution

It provides the first large-scale statistical analysis of asteroid shape distribution using Gaia DR2 data, including correlations with size and other properties.

Findings

Asteroids >50 km are generally rounder than smaller ones.

Average axial ratio b/a is approximately 0.80, consistent with previous studies.

Shape distribution varies with asteroid properties beyond size.

Abstract

Gaia Data Release 2 includes observational data for 14,099 pre-selected asteroids. From the sparsely sampled G band photometry, we derive lower-limit lightcurve amplitudes for 11,665 main belt asteroids in order to provide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for each asteroid, defined through the axial aspect ratios a > b and b=c, we find an average b/a=0.80+-0.04 for the ensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties from the literature, we investigate possible correlations of the aspect ratio with size, semi-major axis, geometric albedo, and intrinsic color. Based on our model simulations, we find that main belt asteroids greater than 50 km in diameter on average have higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences in the shape distribution of main belt asteroids as a function of the other properties that do not affect the average aspect ratios. We conclude that a more detailed investigation of shape distribution correlations requires a larger data sample than is provided in Gaia Data Release 2.