Trans-Neptunian Objects Transiently Stuck in Neptune’s Mean-motion Resonances: Numerical Simulations of the Current Population

Abstract

A substantial fraction of our solar system's trans-Neptunian objects (TNOs) are in mean-motion resonance with Neptune. Many of these objects were likely caught into resonances by planetary migration-either smooth or stochastic-approximately 4 Gyr ago. Some, however, gravitationally scattered off of Neptune and became transiently stuck in more recent events. Here we use numerical simulations to predict the number of transiently stuck objects, captured from the current actively scattering population, that occupy 111 resonances at semimajor axes a = 30-100 au. Our source population is an observationally constrained model of the currently scattering TNOs. We predict that, integrated across all resonances at these distances, the current transient-sticking population comprises 40% of the total transiently stuck+ scattering TNOs, suggesting that these objects should be treated as a single population. We compute the relative distribution of transiently stuck objects across all p: q resonances with 1/6 <= q/p < 1,p < 40, and q < 20, providing predictions for the population of transient objects with H-r < 8.66 in each resonance. We find that the relative populations are approximately proportional to each resonance's libration period and confirm that the importance of transient sticking increases with semimajor axis in the studied range. We calculate the expected distribution of libration amplitudes for stuck objects and demonstrate that observational constraints indicate that both the total number and the amplitude distribution of 5: 2 resonant TNOs are inconsistent with a population dominated by transient sticking from the current scattering disk. The 5: 2 resonance hence poses a challenge for leading theories of Kuiper Belt sculpting.