Dynamical environment and stability around Centaur (2060) Chiron

TL;DR

This study investigates the stability of Chiron's ring system through numerical simulations, revealing that inner rings are ephemeral unless continuously replenished and linking some rings to specific spin-orbit resonances.

Contribution

First dynamical assessment of Chiron's rings, identifying stability zones, resonance links, and the influence of Chiron's shape on ring longevity.

Findings

Inner ring zone is chaotic and short-lived (~1 year) unless replenished.

Outer rings can remain stable for at least a decade.

Certain rings are linked to specific spin-orbit resonances, explaining observed asymmetries.

Abstract

A recent stellar occultation revealed that the Centaur (2060) Chiron hosts a broad disk extending beyond ~200 km from its centre, embedding three ring-like structures (Chi1R, Chi2R, and Chi3R), while a tenuous outer ring (Chi4R) lies beyond the Roche limit. Here, we present a first dynamical assessment of the system's stability through numerical simulations of test particles, accounting for Chiron's triaxial figure. For an equatorial ellipticity of C22~0.02, as inferred from the most recent shape estimates, our simulations reveal a chaotic inner zone extending to ~260 km, where particle lifetimes reach up to a year, while particles beyond ~260 km can remain stable for at least a decade. These results suggest that the innermost portion of the disk is ephemeral and can only persist if continuously replenished. For lower ellipticity values (C22<0.012), however, the entire disk is located within the stable region, regardless of Chiron's mass. Under the physical parameters currently available in the literature, Chi2R is possibly linked to the 1:3 spin-orbit resonance, while Chi1R cannot be linked to the 1:2 resonance, as previously proposed, since this resonance is unstable. Instead, Chi1R and Chi3R may be associated with the 2:5 and 1:5 spin-orbit resonances, respectively. Both the 1:3 and 1:5 resonances are bifurcated, generating chaotic zones that may explain the gap in Chi2R and the longitudinal asymmetry observed in Chi3R.