For planets of a binary star system, in which the 2 stars have equal masses and zero eccentricity, the stable zone for S-type orbits extends continuously to greater than 0.65. and the stable zone for P-type orbits extends continuously to less than 0.55. (The unit used here is the orbital semimajor axis of the planet divided by the orbital semimajor axis of the binary pair). Stable S-type coplanar orbits in the region from approx 0.26 to greater than 0.65 are possible only in the retrograde direction. Stable P-type coplanar orbits in the region from approx 2.0 to less than 0.55 are possible only in the retrograde direction. More generally, for all theoretical or real binary star systems of any mass ratio and eccentricity, for both S-type orbits (in systems where S-type orbits are possible) and P-type orbits, the stable zones are significantly larger for retrograde coplanar orbits than for prograde coplanar orbits.
Copyright 2001 S.Edgeworth