The Kozai mechanism often destabilises high inclination orbits. It coupleschanges in the eccentricity and inclination, and drives high inclination,circular orbits to low inclination, eccentric orbits. In a recent study of thedynamics of planetesimals in the quadruple star system HD98800 (Verrier & Evans2008), there were significant numbers of stable particles in circumbinary polarorbits about the inner binary pair which are apparently able to evade the Kozaiinstability. Here, we isolate this feature and investigate the dynamics throughnumerical and analytical models. The results show that the Kozai mechanism ofthe outer star is disrupted by a nodal libration induced by the inner binarypair on a shorter timescale. By empirically modelling the period of thelibration, a criteria for determining the high inclination stability limits ingeneral triple systems is derived. The nodal libration feature is interestingand, although effecting inclination and node only, shows many parallels to theKozai mechanism. This raises the possibility that high inclination planets andasteroids may be able to survive in multistellar systems.
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