Dynamics of Neptune's Trojans: II. Eccentric orbits and observed ones

TL;DR

This study explores the stability of Neptune Trojans with eccentric orbits, revealing how resonances and secular effects influence their long-term dynamics and assessing the stability of observed Trojans within these dynamical frameworks.

Contribution

It provides detailed dynamical maps of Neptune Trojan stability across eccentricities and inclinations, and analyzes the mechanisms behind their stability and chaos, including resonances and secular effects.

Findings

Maximum stable eccentricities are 0.10, 0.12, and 0.04 for low, medium, and high inclinations.

Most observed Trojans are within stable regions, except for 2001 QR322 and 2005 TO74.

Secondary and secular resonances significantly affect Trojan orbital stability.

Abstract

In a previous paper, we have presented a global view of the stability of Neptune Trojan (NT hereafter) on inclined orbit. We discuss in this paper the dependence of stability of NT orbits on the eccentricity. High-resolution dynamical maps are constructed using the results of extensive numerical integrations of orbits initialized on the fine grids of initial semimajor axis (a0) versus eccentricity (e0). The extensions of regions of stable orbits on the (a0, e0) plane at different inclinations are shown. The maximum eccentricities of stable orbits in three most stable regions at low (0, 12deg.), medium (22,36deg.) and high (51, 59deg.) inclination, are found to be 0.10, 0.12 and 0.04, respectively. The fine structures in the dynamical maps are described. Via the frequency analysis method, the mechanisms that portray the dynamical maps are revealed. The secondary resonances, concerning the frequency of the librating resonant angle and the frequency of the quasi 2:1 mean motion resonance between Neptune and Uranus, are found deeply involved in the motion of NTs. Secular resonances are detected and they also contribute significantly to the triggering of chaos in the motion. Particularly, the effects of the secular resonance v8, v18 are clarified. We also investigate the orbital stabilities of six observed NTs by checking the orbits of hundreds clones of them generated within the observing error bars. We conclude that four of them, except 2001 QR322 and 2005 TO74, are deeply inside the stable region. The 2001 QR322 is in the close vicinity of the most significant secondary resonance. The 2005 TO74 locates close to the boundary separating stable orbits from unstable ones, and it may be influenced by a secular resonance.