On the Dynamical Origins of Retrograde Jupiter Trojans and their Connection to High-Inclination TNOs

Abstract

Over the course of the last decade, observations of highly-inclined (orbital inclination i > 60{\deg}) Trans-Neptunian Objects (TNOs) have posed an important challenge to current models of solar system formation (Levison et al. 2008; Nesvorn\'y 2015). These remarkable minor planets necessitate the presence of a distant reservoir of strongly-out-of-plane TNOs, which itself requires some dynamical production mechanism (Gladman et al. 2009; Gomes et al. 2015; Batygin and Brown 2016). A notable recent addition to the census of high-i minor bodies in the solar system is the retrograde asteroid 514107 Ka'epaoka'awela, which currently occupies a 1:-1 mean motion resonance with Jupiter at i = 163{\deg} (Wiegert et al. 2017). In this work, we delineate a direct connection between retrograde Jupiter Trojans and high-i Centaurs. First, we back-propagate a large sample of clones of Ka'epaoka'awela for 100 Ma numerically, and demonstrate that long-term stable clones tend to decrease their inclination steadily until it concentrates between 90{\deg} and 135{\deg}, while their eccentricity and semi-major axis increase, placing many of them firmly into the trans-Neptunian domain. Importantly, the clones show significant overlap with the synthetic high-i Centaurs generated in Planet 9 studies (Batygin et al. 2019), and hint at the existence of a relatively prominent, steady-state population of minor bodies occupying polar trans-Saturnian orbits. Second, through direct numerical forward-modeling, we delineate the dynamical pathway through which conventional members of the Kuiper Belt's scattered disk population can become retrograde Jovian Trojan resonators in presence of Planet 9.