At http://phys.org/print365330655.html … astrophysicists at the University of Toronto are saying that after a close encounter with Jupiter another, an unknown and unnamed planet was ejected from our solar system after a bumping session. How to eject a planet is interesting as Jupiter has moons and Voyager 1 is struggling to escape from the helio-sheaf. The astrophysicists appear confident it can be achieved as a result of a close encounter causing one of the bodies to accelerate to such an extent which allows it to break free of the gravitational pull of the Sun. It is all modelled of course so I suppose it depends on what was factored into the research. They chose Jupiter over Saturn because the moons of the latter seemed not to favour such an encounter. The original idea of a former planet that has since said goodbye goes back to 2011 and the research was an attempt to see if it was feasible – which is laudable.