Jupiter Trojan Temporary Interlopers and Libration Amplitude Distributions

The Jupiter Trojan population boasts 12,000+ known members. However, due to a limited application of compute-intensive classification algorithms to the large number of known objects in and near the Jupiter Trojans, the Minor Planet Center (MPC)’s simplified classification scheme using osculating element cuts is beginning to show its limitations. The non-rigorous algorithm has resulted in the mis-classification of two objects in/near the Jupiter Trojan population to date: (514107) Ka'epaoka'awela 2015 BZ509 and 2019 LD2. 2015 BZ509 has been identified as a temporarily-captured retrograde jovian co-orbital (Wiegert et al. 2017), however the MPC’s classification algorithm labels it a main-belt asteroid and not a Trojan/transient co-orbital. Due to its recent cometary activity, 2019 LD2 has been identified as an active Centaur transitioning to the inner Solar System (Kareta et al. 2020, Steckloff et al. 2020, & Hsieh et al. 2021), however the MPC classifies it as a primordial Trojan. Due to the lack of accurate identification of objects not long-term stable in/near the Trojans through rigorous resonant analysis, the expectation that as many as 100 asteroids and Centaurs with diameters d>1 km are captured as <a-few-Myr-timescale temporary jovian co-orbitals (Greenstreet et al. 2020), and the ~25x increase in Trojan detections expected by the upcoming (late 2024) Rubin Observatory’s Legacy Survey of Space and Time (LSST; LSST Science Collaboration 2017), we study this sample.

We securely identify the primordial Trojans, transient co-orbitals, and transitionary objects in the known near-Jupiter population. We use numerical integrations of observationally-derived orbits and large numbers of clones within the orbital uncertainty region to search for semimajor axis oscillation around Jupiter’s semimajor axis as well as resonant argument libration for periods of time long enough (>5 kyr) to distinguish transient co-orbital capture or transitionary behavior from primordial Trojan stability (Alexandersen et al. 2013, 2021; Greenstreet et al. 2020).

We present preliminary libration amplitude distributions of all primordial Trojans and transient co-orbitals (in Trojan, horseshoe, quasi-satellite, and retrograde motion) identified to be librating (Levison et al. 1997). These libration amplitudes can be compared with models of early Solar System evolution such as the Grand Tack model of Jupiter’s migration through the inner Solar System (Walsh et al. 2011).

We also discuss the dynamical behavior of transient co-orbitals and transitionary objects identified among the near-Jupiter population.