The Main Belt Asteroid Shape Distribution from Gaia Data Release 2

摘要

Gaia Data Release 2 includes observational data for 14099?pre-selected asteroids. From the sparsely sampledG-band photometry, we derive lower-limit light curve amplitudes for 11665 main belt asteroids (MBA) in order toprovide constraints on the distribution of shapes in the asteroid main belt. Assuming a triaxial shape model for eachasteroid, defined through the axial aspect ratios a > b and b?=?c, we find an average b/a?=?0.80?±?0.04 for theensemble, which is in agreement with previous results. By combining the Gaia data with asteroid properties fromthe literature, we investigate possible correlations of the aspect ratio with size, semimajor axis, geometric albedo,and intrinsic color. Based on our model simulations, we find that MBAs greater than 50?km in diameter on averagehave higher b/a aspect ratios (are rounder) than smaller asteroids. We furthermore find significant differences inthe shape distribution of MBAs as a function of the other properties that do not affect the average aspect ratios. Weconclude that a more detailed investigation of shape distribution correlations requires a larger data sample than isprovided in Gaia Data Release 2.