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

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 $i \lt 40^\circ$. 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 $a\approx 57.9$ au) hosts more resonators, rather than fewer as expected, compared to the lower order, stronger 3:7 MMR (at $a\approx 53.0$ au). Future observations, whether confirming or challenging this phenomenon, will offer valuable insight into the eccentricity and inclination distributions of primordial KBOs.