Neptune's 5:2 Resonance in the Kuiper Belt

TL;DR

This paper investigates Neptune's 5:2 resonance in the Kuiper Belt, revealing phase space structures, resonance widths, and stability conditions through models and simulations, explaining the large population and eccentricity concentration of resonant KBOs.

Contribution

The study provides a detailed analysis of the phase space and stability of Neptune's 5:2 resonance, combining theoretical models with N-body simulations to explain observed KBO properties.

Findings

Resonance width peaks near eccentricity 0.4

Stable resonance zone boundaries are insensitive to inclination

High eccentricity orbits above 0.53 are unstable

Abstract

Observations of Kuiper belt objects (KBOs) in Neptune's 5:2 resonance present two puzzles: this third order resonance hosts a surprisingly large population, comparable to the prominent populations of Plutinos and Twotinos in the first order 3:2 and 2:1 resonances, respectively; secondly, their eccentricities are concentrated near $0.4$. To shed light on these puzzles, we investigate the phase space near this resonance with use of Poincar\'e sections of the circular planar restricted three body model. We find several transitions in the phase space structure with increasing eccentricity, which we explain with the properties of the resonant orbit relative to Neptune's. The resonance width is narrow for very small eccentricities, but widens dramatically for $e\gtrsim0.2$, reaching a maximum near $e\approx0.4$, where it is similar to the maximum widths of the 2:1 and 3:2 resonances. We confirm these results with N-body numerical simulations, including the effects of all four giant planets and a wide range of orbital inclinations of the KBOs. We find that the boundaries of the stable resonance zone are not strongly sensitive to inclination and remain very similar to those found with the simplified three body model, with the caveat that orbits of eccentricity above $\sim0.53$ are unstable; higher eccentricity orbits are phase-protected from destabilizing encounters with Neptune but not with Uranus. These results show that the 5:2 resonant KBOs are not more puzzling than the Plutinos and Twotinos; however, detailed understanding of the origins of eccentric, inclined resonant KBOs remains a challenge.