A systematic survey of the dynamics of Uranus Trojans

TL;DR

This paper systematically maps the stability regions of Uranus Trojans, identifies the dynamical mechanisms shaping their phase space, and assesses their survival rates during planetary migration.

Contribution

It provides a detailed dynamical map of Uranus Trojans, revealing stability regions, resonance effects, and survival probabilities during planetary migration.

Findings

Two main stability regions identified for UTs at low and high inclinations.

Most long-lived UTs are low-inclined, comprising 77% of surviving orbits.

Approximately 3.81% of initial UTs survive the solar system's age, mostly at low inclinations.

Abstract

We aim to locate the stability region for Uranus Trojans (UT hereafter) and find out the dynamical mechanisms responsible for the structures in the phase space. Using the spectral number as the stability indicator, we construct the dynamical maps on the (a0, i0) plane. The proper frequencies of UTs are determined precisely so that we can depict the resonance web via a semi-analytical method. Two main stability regions are found, one each for the low-inclination (0-14deg) and high-inclination regime (32-59deg). There is also an instability strip in each of them, at 9deg and 51deg respectively. All stability regions are in the tadpole regime and no stable horseshoe orbits exist for UTs. The lack of moderate-inclined UTs is caused by the nu5 and nu7 secular resonances. The fine structures in the dynamical maps are shaped by high-degree secular resonances and secondary resonances. During the planetary migration, about 36.3% and 0.4% of the pre-formed orbits survive the fast and slow migrations (with migrating time scales of 1 and 10Myr) respectively, most of which are in high inclination. Since the low-inclined UTs are more likely to survive the age of the solar system, they make up 77% of all such long-life orbits by the end of the migration, making a total fraction up to 4.06E-3 and 9.07E-5 of the original population for the fast and slow migrations, respectively. About 3.81% UTs are able to survive the age of the solar system, among which 95.5% are on low-inclined orbits with i0<7.5deg. However, the depletion of the planetary migration seems to prevent a large fraction of such orbits, especially for the slow migration model.