On the oldest asteroid families in the main belt

TL;DR

This study investigates the age and stability of the oldest asteroid families in the main belt, finding none older than 2.7 billion years under standard Yarkovsky assumptions, and exploring implications for early Solar System history.

Contribution

The paper provides a dynamical analysis of seven ancient asteroid families, estimating their maximum ages and discussing the detectability of paleo-families formed over 2.7 Gyr ago.

Findings

No family older than 2.7 Gyr under standard Yarkovsky parameters.

Older paleo-families would have shallow size distributions and be detectable only in less active regions.

V-type asteroids may originate from a paleo-Eunomia family.

Abstract

Asteroid families are groups of minor bodies produced by high-velocity collisions. After the initial dispersions of the parent bodies fragments, their orbits evolve because of several gravitational and non-gravitational effects,such as diffusion in mean-motion resonances, Yarkovsky and YORP effects, close encounters of collisions, etc. The subsequent dynamical evolution of asteroid family members may cause some of the original fragments to travel beyond the conventional limits of the asteroid family. Eventually, the whole family will dynamically disperse and no longer be recognizable. A natural question that may arise concerns the timescales for dispersion of large families. In particular, what is the oldest still recognizable family in the main belt? Are there any families that may date from the late stages of the Late Heavy Bombardment and that could provide clues on our understanding of the primitive Solar System? In this work, we investigate the dynamical stability of seven of the allegedly oldest families in the asteroid main belt. Our results show that none of the seven studied families has a nominally mean estimated age older than 2.7 Gyr, assuming standard values for the parameters describing the strength of the Yarkovsky force. Most "paleo-families" that formed between 2.7 and 3.8 Gyr would be characterized by a very shallow size-frequency distribution, and could be recognizable only if located in a dynamically less active region (such as that of the Koronis family). V-type asteroids in the central main belt could be compatible with a formation from a paleo-Eunomia family.