A six-part collisional model of the main asteroid belt

TL;DR

This paper develops a detailed six-part collisional model of the main asteroid belt, testing scaling laws, initial size distributions, and asteroid compositions to match observed data and asteroid family counts.

Contribution

It introduces a new six-part model incorporating hydrodynamic simulation results, and distinguishes between monolithic and rubble-pile asteroids to better fit observed size-frequency distributions.

Findings

Majority of main-belt asteroids are monolithic.

Rubble-pile model fits observed data worse.

Dynamical depletion by Yarkovsky effect is significant.

Abstract

In this work, we construct a new model for the collisional evolution of the main asteroid belt. Our goals are to test the scaling law of Benz and Asphaug (1999) and ascertain if it can be used for the whole belt. We want to find initial size-frequency distributions (SFDs) for the considered six parts of the belt (inner, middle, 'pristine', outer, Cybele zone, high-inclination region) and to verify if the number of synthetic asteroid families created during the simulation matches the number of observed families as well. We used new observational data from the WISE satellite (Masiero et al., 2011) to construct the observed SFDs. We simulate mutual collisions of asteroids with a modified version of the Boulder code (Morbidelli et al., 2009), where the results of hydrodynamic (SPH) simulations of Durda et al. (2007) and Benavidez et al. (2012) are included. Because material characteristics can significantly affect breakups, we created two models - for monolithic asteroids and for rubble-piles. To explain the observed SFDs in the size range D = 1 to 10 km we have to also account for dynamical depletion due to the Yarkovsky effect. The assumption of (purely) rubble-pile asteroids leads to a significantly worse fit to the observed data, so that we can conclude that majority of main-belt asteroids are rather monolithic. Our work may also serve as a motivation for further SPH simulations of disruptions of smaller targets (with a parent body size of the order of 1 km).