We have been discovering planets outside our Solar System at an impressive rate. Most are Jupiter size or larger. I was wondering how diverse planitary systems could be about other stars.
Is it likely that all planetary orbits are in a plane that is prety much perpendiculsr to the rotational axis of the parent star, as are those or our Solar System (Pluto is a slight exception)? Would orbits at drasticly different angles be stable? How about two ro more planets on the same orbit? ... or three Earthlike planets at close LaGrange points?
Such arrangements, if gravitationally possible would make for close Earthlike planets in a star system and short space-hops for a civilization evolving on any one of such planets.