The disturbing function for polar Centaurs and transneptunian objects

TL;DR

This paper develops a new series expansion of the gravitational disturbing function suitable for nearly polar orbits, enabling better analysis of resonances in Centaurs and transneptunian objects.

Contribution

It introduces a polar disturbing function expansion to fourth order, differing from classical models, allowing accurate resonance analysis for nearly polar orbits.

Findings

Polar disturbing function can model any resonance regardless of order.

Resonance amplitude depends on parity of the resonance order.

Application to specific resonances shows potential locking of a transneptunian object.

Abstract

The classical disturbing function of the three-body problem is based on an expansion of the gravitational interaction in the vicinity of nearly coplanar orbits. Consequently, it is not suitable for the identification and study of resonances of the Centaurs and transneptunian objects on nearly polar orbits with the solar system planets. Here, we provide a series expansion algorithm of the gravitational interaction in the vicinity of polar orbits and produce explicitly the disturbing function to fourth order in eccentricity and inclination cosine. The properties of the polar series differ significantly from those of the classical disturbing function: the polar series can model any resonance as the expansion order is not related to the resonance order. The powers of eccentricity and inclination of the force amplitude of a $p$:$q$ resonance do not depend on the value of the resonance order $|p-q|$ but only on its parity. Thus all even resonance order eccentricity amplitudes are $\propto e^2$ and odd ones $\propto e$ to lowest order in eccentricity $e$. With the new findings on the structure of the polar disturbing function and the possible resonant critical arguments, we illustrate the dynamics of the polar resonances 1:3, 3:1, 2:9 and 7:9 where transneptunian object 471325 could currently be locked.