# Not a simple relationship between Neptune's migration speed and Kuiper belt inclination excitation

## TL;DR

Numerical simulations show that Neptune's migration speed does not have a consistent effect on Kuiper belt inclination excitation, challenging previous assumptions and highlighting the importance of planetary secular architecture.

## Contribution

This study demonstrates that inclination excitation in the Kuiper belt is independent of Neptune's migration timescale, emphasizing the role of planetary secular modes over migration speed.

## Key findings

- Inclination dispersion can be achieved with various migration timescales.
- No clear correlation between migration speed and inclination excitation.
- Differences in planetary secular architecture influence inclination outcomes.

## Abstract

We present numerical simulations of giant planet migration in our solar system and examine how the speed of planetary migration affects inclinations in the resulting population of small bodies (test particles) scattered outward and subsequently captured into Neptune's 3:2 mean motion resonance (the Plutinos) as well as the hot classical Kuiper belt population. We do not find a consistent relationship between the degree of test particle inclination excitation and e-folding planet migration timescales in the range 5-50 Myr. Our results present a counter-example to Nesvorny 2015's finding that the Plutino and hot classical inclinations showed a marked increase with increasing e-folding timescales for Neptune's migration. We argue that these differing results are likely due to differing secular architectures of the giant planets during and after migration. Small changes in the planets' initial conditions and differences in the numerical implementation of planet migration can result in different amplitudes of the planets' inclination secular modes, and this can lead to different final inclination distributions for test particles in the simulations. We conclude that the observed large inclination dispersion of Kuiper belt objects does not require Neptune's migration to be slow; planetary migration with e-folding timescales of 5, 10, 30, and 50 Myr can all yield inclination dispersions similar to the observed Plutino and hot classical populations, with no correlation between the degree of inclination excitation and migration speed.