Gyr-timescale destruction of high-eccentricity asteroids by spin and why 2006 HY51 has been spared

TL;DR

This study introduces a fast simulation method to analyze the long-term spin evolution of highly eccentric asteroids, revealing that 2006 HY51 is unlikely to undergo rotational breakup despite chaotic spin states.

Contribution

A novel 1D simulation approach enabling the study of asteroid spin evolution over billions of orbits, applied to 2006 HY51 and potential exo-asteroids.

Findings

2006 HY51 cannot reach rotational break-up speed

Primordial asteroids on more eccentric orbits may have already broken up

Method allows long-term evolution analysis of highly eccentric exo-asteroids

Abstract

Asteroids and other small celestial bodies have markedly prolate shapes, and the perturbative triaxial torques which are applied during pericenter passages in highly eccentric orbits trigger and sustain a state of chaotic rotation. Because the prograde spin rate around the principal axis of inertia is not bounded from above, it can accidentally reach the threshold value corresponding to rotational break-up. Previous investigations of this process were limited to integrations of $\sim 10^3$ orbits because of the stiff equation of motion. We present here a fast 1D simulation method to compute the evolution of this spin rate over $\sim 10^9$ orbits. We apply the method to the most eccentric solar system asteroid known, 2006 HY51 (with $e = 0.9684$), and find that for any reasonably expected shape parameters, it can never be accelerated to break-up speed. However, primordial solar system asteroids on more eccentric orbits may have already broken up from this type of rotational fission. The method also represents a promising opportunity to investigate the long-term evolution of extremely eccentric triaxial exo-asteroids ($e > 0.99$), which are thought to be common in white dwarf planetary systems