Inclination Mixing in the Classical Kuiper Belt

TL;DR

This study explores the long-term inclination evolution of Kuiper Belt objects, revealing that their inclinations can vary significantly over gigayear timescales due to Neptune encounters and resonance chaos, affecting their physical property correlations.

Contribution

It demonstrates that Kuiper Belt object inclinations are highly variable over time, challenging previous assumptions about their static nature and their correlation with physical properties.

Findings

Classical KBOs can experience large inclination changes over gigayears.

Resonant KBOs show greater inclination variability and less stability.

Inclination variability affects correlations with physical properties.

Abstract

We investigate the long-term evolution of the inclinations of the known classical and resonant Kuiper belt objects (KBOs). This is partially motivated by the observed bimodal inclination distribution and by the putative physical differences between the low- and high-inclination populations. We find that some classical KBOs undergo large changes in inclination over gigayear timescales, which means that a current member of the low-inclination population may have been in the high-inclination population in the past, and vice versa. The dynamical mechanisms responsible for the time-variability of inclinations are predominantly distant encounters with Neptune and chaotic diffusion near the boundaries of mean motion resonances. We reassess the correlations between inclination and physical properties including inclination time-variability. We find that the size-inclination and color-inclination correlations are less statistically significant than previously reported (mostly due to the increased size of the data set since previous works with some contribution from inclination variability). The time-variability of inclinations does not change the previous finding that binary classical KBOs have lower inclinations than non-binary objects. Our study of resonant objects in the classical Kuiper belt region includes objects in the 3:2, 7:4, 2:1, and eight higher-order mean motion resonances. We find that these objects (some of which were previously classified as non-resonant) undergo larger changes in inclination compared to the non-resonant population, indicating that their current inclinations are not generally representative of their original inclinations. They are also less stable on gigayear timescales.