A study of the high-inclination population in the Kuiper belt -- V. Mean motion resonances beyond 50 AU

TL;DR

This comprehensive study investigates Neptune's mean-motion resonances in the distant Kuiper belt from 50 to 100 AU, revealing the potential for KBOs to occupy high-order resonances and uncovering new dynamical phenomena.

Contribution

It provides the most detailed analysis to date of MMRs beyond 50 AU, including a database of resonance characteristics and long-term stability simulations, highlighting the existence of high-order resonators and a novel number reversal phenomenon.

Findings

Resonators occupy all 1:n to 7:n MMRs in the 50-100 AU region.

Inclinations up to 40° and eccentricities below 0.7 are common among resonators.

Discovery of a number reversal phenomenon where higher-order MMRs host more resonators.

Abstract

In this paper, we present the most comprehensive study to date on Neptune's mean-motion resonances (MMRs) in the distant Kuiper belt from 50 to 100 AU. Over 200 resonant Kuiper belt objects (KBOs) have been identified in this region, spanning resonances from the 2nd-order 1:3 MMR to the 22nd-order 7:29 MMR, with inclinations $i<40^\circ$. Building on these diverse distributions, we first analyse the dynamical features of numerous $m$:$n$ MMRs, providing an informative database that includes the possible eccentricity ($e$) range, resonance widths, resonance centres, and permissible $(e,i)$ distributions. We then conduct numerical simulations to explore the long-term stability of these MMRs. Our results show that: (1) resonators can occupy all 1:$n$ to 7:$n$ MMRs, with nearly any $n$ corresponding to the 50-100 AU region, including the farthest-out MMRs of 5:29 (24th-order), 6:35 (29th-order), and 7:40 (33rd-order). This suggests that KBOs could potentially exist in even higher-order MMRs than those currently observed. (2) For each set of $m$:$n$ resonances with the same $m$, resonators consistently exhibit inclinations up to $40^\circ$, while eccentricities remain strictly restricted below 0.7. (3) For the 1:3 and 1:4 MMRs, the leading population is less stable than the trailing population. Most interestingly, we discover a novel phenomenon of number reversal, where the higher-order, weaker 3:8 MMR (at semimajor axis $a\approx57.9$ AU) hosts more resonators, rather than fewer as expected, compared to the lower-order, stronger 3:7 MMR (at $a\approx53.0$ AU). Future observations, whether confirming or challenging this phenomenon, will offer valuable insight into the eccentricity and inclination distributions of primordial KBOs.