High Inclination Planets in Multistellar Systems

TL;DR

This paper investigates how high inclination planets can remain stable in multistellar systems by analyzing the disruption of the Kozai mechanism through nodal libration, revealing potential for stable high inclination orbits.

Contribution

It introduces a new stability criterion for high inclination orbits in triple star systems based on numerical and analytical models of nodal libration.

Findings

Nodal libration can disrupt Kozai cycles in triple systems.

High inclination stable orbits can survive due to libration effects.

A stability criterion for high inclination orbits is derived.

Abstract

The Kozai mechanism often destabilises high inclination orbits. It couples changes in the eccentricity and inclination, and drives high inclination, circular orbits to low inclination, eccentric orbits. In a recent study of the dynamics of planetesimals in the quadruple star system HD98800 (Verrier & Evans 2008), there were significant numbers of stable particles in circumbinary polar orbits about the inner binary pair which are apparently able to evade the Kozai instability. Here, we isolate this feature and investigate the dynamics through numerical and analytical models. The results show that the Kozai mechanism of the outer star is disrupted by a nodal libration induced by the inner binary pair on a shorter timescale. By empirically modelling the period of the libration, a criteria for determining the high inclination stability limits in general triple systems is derived. The nodal libration feature is interesting and, although effecting inclination and node only, shows many parallels to the Kozai mechanism. This raises the possibility that high inclination planets and asteroids may be able to survive in multistellar systems.