  A widely considered characteristic of extra-solar planetary systems has been
a seeming tendency for major axes of adjacent orbits to librate in stable
configurations. Based on a new catalog of extra-solar planets (Butler et al.
2006) and our numerical integrations, we find that such small amplitude
oscillations are actually not common, but in fact quite rare; most pairs of
planets' major axes a re consistenet with circulating relative to one another.
However, the new result s are consistent with studies that find that two-planet
systems tend to lie near a separatrix between libration and circulation.
Similarly, in systems of more than two planets, many adjacent orbits lie near a
separatrix that divides modes of circulation.
