How variations in giant planet migration simulations affect predicted resonant transneptunian populations

The observed populations of transneptunian objects (TNOs) in Neptune’s mean motion resonances provide important clues about the nature and extent of giant planet migration in our solar system’s early history. To test scenarios for the dynamical histories of the giant planets, we rely on numerical simulations that approximate different migration histories for the planets and track how test particles representing primordial TNOs end up distributed once the giant planets arrive at their final locations. But there remain several questions not satisfactorily answered in the current literature about whether simulations of migration scenarios produce acceptably consistent predictions to compare to the real, observed TNO distributions: 1) how closely do the end states of the simulated giant planets’ orbits need to resemble the orbits of the real, present day giant planets for the simulation?, and 2) how much do the numerical methods used to achieve those final orbits (usually via fictitious forces in the orbit integrator) matter? Modelers typically impose some range in giant planet period ratios and eccentricity ranges in deciding whether a migration simulation output is “acceptable”, but how to define this acceptability has not been examined in much detail, even in the simplest case of smooth outward giant planet migration. Similarly, the effects of how one gets to those final orbits in these simplified simulations, including whether and how the eccentricities and inclinations of the planets are damped by imposed forces, has not been fully explored. We will present a suite of smooth planet migration simulations with variations in the forces applied to the planets during migration and variations in their final orbit, By examining the detailed distribution of resonant particles captured in these simulations via resonance sweeping, we can determine which aspects of the simulation implementations and the final giant planet system architecture are most important to replicate in migration simulations. We focus on resonance sweeping because it is a very efficient capture mechanism, allowing us to explore a wide range of simulations with a large number of captured test particles at relatively modest computational cost. The lessons learned from these simulations can then guide future explorations of the less-efficient resonant capture mechanisms in the more complicated giant planet migration scenarios that are needed to reproduce many of the observed features of the resonant TNO populations.

This work is supported by NASA Emerging Worlds grant 80NSSC21K0376.