Characterizing the original ejection velocity field of the Koronis family

TL;DR

This study estimates the original ejection velocities of Koronis asteroid family fragments by analyzing their current orbital distribution, accounting for dynamical effects, and finds that ejection speeds are inversely proportional to fragment size with a minimum of about 50 m/s.

Contribution

It introduces a method to infer the original ejection velocity field of the Koronis family from current orbital data, considering dynamical perturbations.

Findings

Ejection speeds are inversely proportional to fragment size within 15% error.

Minimum ejection velocity is approximately 50 m/s.

Larger ejection velocities are possible depending on initial orbital conditions.

Abstract

An asteroid family forms as a result of a collision between an impactor and a parent body. The fragments with ejection speeds higher than the escape velocity from the parent body can escape its gravitational pull. The cloud of escaping debris can be identified by the proximity of orbits in proper element, or frequency, domains. Obtaining estimates of the original ejection speed can provide valuable constraints on the physical processes occurring during collision, and used to calibrate impact simulations. Unfortunately, proper elements of asteroids families are modified by gravitational and non-gravitational effects, such as resonant dynamics, encounters with massive bodies, and the Yarkovsky effect, such that information on the original ejection speeds is often lost, especially for older, more evolved families. It has been recently suggested that the distribution in proper inclination of the Koronis family may have not been significantly perturbed by local dynamics, and that information on the component of the ejection velocity that is perpendicular to the orbital plane ($v_W$), may still be available, at least in part. In this work we estimate the magnitude of the original ejection velocity speeds of Koronis members using the observed distribution in proper eccentricity and inclination, and accounting for the spread caused by dynamical effects. Our results show that i) the spread in the original ejection speeds is, to within a 15% error, inversely proportional to the fragment size, and ii) the minimum ejection velocity is of the order of 50 m/s, with larger values possible depending on the orbital configuration at the break-up.