Producing wide offset planets from fly-bys on initially stable planetary systems
Recent observations have revealed a population of planets with separations larger than 100 au from their host stars (see, for example, Kalas et al. 2008; Marois et al. 2008). These planets need not have formed at such large separations. Instead they may, for example, have been put there by planet-planet scatterings in planetary systems with planets on initially tight and unstable orbits (Scharf & Menou 2009; Veras, Crepp & Ford 2009). Here we explore an alternative to systems which form with planets on unstable orbits. We consider systems which are stable if left alone, but which become unstable by the interaction with a passing star in a fly-by. This causes strong planet-planet scatterings to occur, which in turn produce wide offset planets (Malmberg, Davies & Heggie 2009, in prep.). Thus, planetary systems which would otherwise be stable will also contribute to the population of wide offset planets.