Just watching "Alien Solar Systems" now. Quite amazing how they believe that Uranus and Neptune's orbits maybe have been different originally and much closer to the sun but that the combined gravity of Saturn and Jupiter threw their orbits further out. They also discuss the possibility of Neptune having been in a closer orbit than Uranus and that they may have crossed paths as both Neptune and Uranus were pushed further out by Jupiter and Saturn.
Or at least that's what I concluded they meant, I don't know much about this stuff to excuse me if I'm wrong
