New asteroid clusters and evidence of collisional fragmentation in the L5 Trojan cloud of Mars

TL;DR

This study re-examines Mars Trojan asteroids, revealing new clusters likely formed from collisional fragmentation and confirming the influence of radiation forces on their orbital evolution.

Contribution

The paper provides a new proper element catalogue for Mars Trojans and identifies two significant asteroid clusters, suggesting their origins from collisional events and rotational breakup.

Findings

Identified two asteroid clusters with 95% confidence.

One cluster likely resulted from rotational breakup of Eureka.

The other cluster is consistent with impact ejecta from Eureka.

Abstract

Context. Trojan asteroids of Mars date from an early phase of solar system evolution. Based on a sample of <10 asteroids, MT distribution has been previously shown to be both asymmetric and inhomogeneous with population evolution dominated by thermal radiation forces acting over timescales of Gyr. Remarkably, a single asteroid family associated with (5261) Eureka (H~16) at L5 contains most MTs and all members of the stable population fainter than H=18. Aims. Using the currently available sample of MTs and their orbits, we take a fresh look at this population to re-evaluate these earlier conclusions and to search for additional features diagnostic of the evolutionary history of MTs and the Eureka family in particular. Methods. We perform harmonic analysis on numerical time series of the osculating elements to compile a new proper element catalogue comprising 16 L5 and 1 L4 Mars Trojan asteroids. We then combine sample variance analysis with statistical hypothesis testing to identify clusters in the distribution of orbits and assess their significance. Results. We identify two small clusterings significant at 95% confidence of three H=20-21 asteroids each and investigate their likely origin. One of the clusters is probably the result of rotational breakup of a Eureka family asteroid ~10^8 yr ago. The significantly higher tadpole libration width of asteroids in the other cluster is more consistent with an origin as impact ejecta from Eureka itself and on a timescale comparable to the ~1 Gyr age of its family. We further confirm the previously reported correlations in Eureka family orbital distribution attributed to the long-term action of radiation-driven forces and torques on the asteroids.