  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.
