Searching for the first Near-Earth Object family

TL;DR

This study searched for genetically related near-Earth asteroid families using clustering techniques and statistical significance tests, but found no conclusive evidence of such families in the current NEO population.

Contribution

The paper applies a novel clustering and significance assessment method to NEOs, providing the first systematic search for NEO families and establishing their apparent absence.

Findings

No statistically significant NEO families were identified.

The most significant cluster had only 2σ significance, insufficient for a family.

Multiple tests did not confirm any cluster as a genetic family.

Abstract

We report on our search for genetically related asteroids amongst the near-Earth object (NEO) population - families of NEOs akin to the well known main belt asteroid families. We used the technique proposed by Fu et al. (2005) supplemented with a detailed analysis of the statistical significance of the detected clusters. Their significance was assessed by comparison to identical searches performed on 1,000 'fuzzy-real' NEO orbit distribution models that we developed for this purpose. The family-free 'fuzzy-real' NEO models maintain both the micro and macro distribution of 5 orbital elements (ignoring the mean anomaly). Three clusters were identified that contain four or more NEOs but none of them are statistically significant at \geq 3{\sigma}. The most statistically significant cluster at the \sim 2{\sigma} level contains 4 objects with H < 20 and all members have long observational arcs and concomitant good orbital elements. Despite the low statistical significance we performed several other tests on the cluster to determine if it is likely a genetic family. The tests included examining the cluster's taxonomy, size-frequency distribution, consistency with a family-forming event during tidal disruption in a close approach to Mars, and whether it is detectable in a proper element cluster search. None of these tests exclude the possibility that the cluster is a family but neither do they confirm the hypothesis. We conclude that we have not identified any NEO families.