Long term dynamics beyond Neptune: secular models to study the regular motions

TL;DR

This paper introduces two semi-analytical secular models for studying the long-term dynamics of small bodies beyond Neptune, focusing on non-resonant and resonant trajectories, with improved accuracy and applicability to planetary systems.

Contribution

The paper develops two new secular models that accurately describe exterior transneptunian object dynamics, including resonance effects, surpassing previous models in precision and generality.

Findings

Maximum perihelion excursion of 16.4 AU identified.

High amplitude perihelion oscillations possible in resonant cases.

Models applicable to any quasi-circular, coplanar planetary system.

Abstract

Two semi-analytical one-degree-of-freedom secular models are presented for the motion of small bodies beyond Neptune. A special attention is given to trajectories entirely exterior to the planetary orbits. The first one is the well-known non-resonant model of Kozai (1962) adapted to the transneptunian region. Contrary to previous papers, the dynamics is fully characterized with respect to the fixed parameters. A maximum perihelion excursion possible of 16.4 AU is determined. The second model handles the occurrence of a mean-motion resonance with one of the planets. In that case, the one-degree-of-freedom integrable approximation is obtained by postulating the adiabatic invariance, and is much more general and accurate than previous secular models found in the literature. It brings out in a plain way the possibility of perihelion oscillations with a very high amplitude. Such a model could thus be used in future studies to deeper explore that kind of motion. For complex resonant orbits (especially of type 1:k), a segmented secular description is necessary since the trajectories are only "integrable by parts". The two models are applied to the Solar System but the notations are kept general so that it could be used for any quasi-circular and coplanar planetary system.