Matching asteroid population characteristics with a model constructed from the YORP-induced rotational fission hypothesis

TL;DR

This study models asteroid populations based on the YORP-induced rotational fission hypothesis, successfully matching observed statistics of small asteroids, binaries, and contact binaries, and providing insights into binary formation and evolution.

Contribution

It integrates the rotational fission hypothesis into an asteroid population model constrained by previous work, with only two free parameters, to explain observed asteroid binary characteristics.

Findings

High mass ratio binaries are four to eight times more frequent than low mass ratio binaries.

The model reproduces observed binary fractions and contact binary statistics.

Post-fission binary mass ratios follow a flat or shallow distribution, contrasting with the steeper observed distribution.

Abstract

From the results of a comprehensive asteroid population evolution model, we conclude that the YORP-induced rotational fission hypothesis can be consistent with the observed population statistics of small asteroids in the main belt including binaries and contact binaries. The foundation of this model is the asteroid rotation model of Marzari et al. (2011), which incorporates both the YORP effect and collisional evolution. This work adds to that model the rotational fission hypothesis and the binary evolution model of Jacobson & Scheeres (2011). The asteroid population evolution model is highly constrained by these and other previous works, and therefore it has only two significant free parameters: the ratio of low to high mass ratio binaries formed after rotational fission events and the mean strength of the binary YORP (BYORP) effect. We successfully reproduce characteristic statistics of the small asteroid population: the binary fraction, the fast binary fraction, steady-state mass ratio fraction and the contact binary fraction. We find that in order for the model to best match observations, rotational fission produces high mass ratio ($> 0.2$) binary components with four to eight times the frequency as low mass ratio ($< 0.2$) components, where the mass ratio is the mass of the secondary component divided by the mass of the primary component. This is consistent with post-rotational fission binary system mass ratio being drawn from either a flat or a positive and shallow distribution, since the high mass ratio bin is four times the size of the low mass ratio bin; this is in contrast to the observed steady-state binary mass ratio, which has a negative and steep distribution. This can be understood in the context of the BYORP-tidal equilibrium hypothesis, which predicts that low mass ratio binaries survive for a significantly longer period of time than high mass ratio systems.