CMoore>The figure-8 orbit is _slightly_ stable, in the sense that small perturbations of the initial positions and momenta, or small changes in the masses away from them being identical, result in smooth oscillations, phase changes, or rotations rather than escape. The same seems to be true of the "criss-cross" orbit, which was discovered by Henon; see some numerical evidence of this in http://arxiv.org/pdf/math/0511219.pdf . Still, you would have to be incredibly lucky to be in the basin of attraction of either orbit. Cris On Mar 9, 2013, at 9:57 PM, Henry Baker wrote: Are there any 3-body configurations that show anything like this type of stability, other than a hierarchy like Sun, Earth, Moon ? Cristopher Moore Professor, Santa Fe Institute ------ Since there's a (small) continuum of possible perturbations, is there a continuum of possible oscillation periods, mostly incommensurable with the main orbits? More generally, are there concrete examples of "immortal", aperiodic three body systems with comparable masses that never eject one? --rwg