On the Influence of Pluto on Twotino Dynamics Through Their Mutual 4:3 Mean Motion Resonance

TL;DR

The study addresses how Pluto influences Twotino dynamics via a previously underappreciated 4:3 mean motion resonance. Using high-resolution 10 Myr N-body simulations with the Sun, the four giant planets, and Pluto, the authors show that Twotinos in the Neptune 2:1 MMR are coupled to Pluto through a 4:3 resonance, with resonant angles librating and a range of amplitudes indicating a diluted but dynamically meaningful effect. They demonstrate that Pluto’s resonance confines co-rotating angles and can enhance orbital perturbations on secular timescales, significantly reducing long-term Twotino stability compared to scenarios without Pluto. A comparison with Eris demonstrates Pluto’s perturbative influence dominates despite Eris’ greater mass. The results argue for including Pluto in dynamical models of the trans-Neptunian region, given its non-negligible impact on resonant populations and secular evolution.

Abstract

Context: The role of Pluto contributing to the long-term evolution of the trans-Neptunian region has been considered significant only over its neighboring Plutinos. However, it has recently been found that the long-term stability of the Twotino population is strongly affected when including Pluto as a massive object in simulations, while Eris, with a similar mass, has a negligible effect. Aims: We hypothesize that the effect of Pluto on Twotinos results from the latter being trapped in a 4:3 mean motion resonance (MMR) with Pluto. In this work, we aim to demonstrate the resonant behavior of Twotinos within Pluto's 4:3 MMR and the significance of this resonance for the long-term evolution of the population. Methods: We run high-resolution, 10 Myr REBOUND simulations of the observed Twotino population in the Kuiper belt, under the perturbations of the Sun, the four giant planets, and Pluto, as massive objects. Results: We find that all objects trapped in the 2:1 MMR with Neptune are locked in a weak 4:3 MMR with Pluto. The 4:3 resonant angles of most objects trapped in the leading and trailing islands of the 2:1 MMR, librate with amplitudes lower than $360^\circ$. Objects in the symmetric islands of the 2:1 MMR librate in the 4:3 MMR with amplitudes greater than $360^\circ$, but, contrary to circulating objects, will oscillate by up to $840^\circ$ visiting preferred angles on Pluto's co-rotating frame, indicating a diluted resonant effect that may also perturb their orbits on secular timescales. Conclusions: The importance of Pluto in shaping the structure of the trans-Neptunian region should be reconsidered, especially for resonant populations. Moreover, with current computational power, its exclusion from simulations can not be justified.

Figures (2)

• Figure 1: Evolution of the 2:1 resonant arguments with respect to Neptune (top panel) and the 4:3 resonant arguments with respect to Pluto (bottom panel) for four selected objects. The blue ($2015\,{\rm VH}_{166}$, leading), green ($2015\,{\rm GZ}_{54}$, trailing), and red ($2015\,{\rm KX}_{173}$, symmetric) curves show the behavior in the three possible Twotino libration islands. The gray curve shows a circulating ($1999\,{\rm RX}_{215}$, non-resonant) object. The vertical dashed line is placed at $62,000$ yr, representing one libration period of the symmetric object.
• Figure 2: Co-rotational orbits with respect to Pluto of the four sample Twotinos (top panels) over 1 Myr, as well as the measured probability distribution function to find each Twotino at a certain co-rotating angle (bottom panels). The black curves represent Pluto's orbit in the co-rotational frame, while colored curves represent each Twotino, following the same color scheme as Figure \ref{['fig:phitime']}. To see the evolution of the orbit, see the attached animation of these four objects on the https://github.com/Sramrev/Pluto-Twotino-MMR.git repository.