Jupiter's Metastable Companions

TL;DR

This study uses extensive numerical simulations to reveal that many Jovian co-orbitals, including Trojans, horseshoe orbits, and quasi-satellites, are metastable and recently captured, challenging the view of Trojans as solely primordial.

Contribution

First identification of metastable Jovian co-orbitals, including Trojans, horseshoe, and quasi-satellites, showing a dynamic steady-state population.

Findings

Many Trojans are recent captures, not primordial.

Discovered long-lived horseshoe co-orbitals.

Identified metastable quasi-satellites with lifetimes up to 130 kyr.

Abstract

Jovian co-orbitals share Jupiter's orbit in 1:1 mean motion resonance. This includes $>$10,000 so-called Trojan asteroids surrounding the leading (L4) and trailing (L5) Lagrange points, viewed as stable groups dating back to planet formation. Via a massive numerical study we identify for the first time some Trojans which are certainly only `metastable'; instead of being primordial, they are recent captures from heliocentric orbits into moderately long-lived (10 kyr - 100 Myr) metastable states that will escape back to the scattering regime. We have also identified (1) the first two jovian horseshoe co-orbitals that exist for many resonant libration periods, and (2) eight jovian quasi-satellites with metastable lifetimes of 4-130 kyr. Our perspective on the Trojan population is thus now more complex as Jupiter joins the other giant planets in having known metastable co-orbitals which are in steady-state equilibrium with the planet-crossing Centaur and asteroid populations, in agreement with theoretical estimates.