Planetary systems orbiting stars in young stellar clusters are vulnerable to the effects of fly-bys. We here consider fly-bys involving planetary systems with gas giants on orbits similar to those of the gas giants in the Solar System. In very close fly-bys the effect may be to immediately unbind one or more planets. However, an exchange may also occur, in which one or more planets become bound to the intruding star immediately after the fly-by (Malmberg, Davies & Heggie, in prep.). Such exchanges can produce planets on very wide and moderately eccentric orbits, similar to the planets detected in recent imaging surveys (e.g. Kalas et al. 2008). In wider fly-bys the effect is most often to only perturb the orbits of the planets, which can however lead to planet-planet scatterings in the system. These may result in the ejection of one or more planets, leaving those remaining on tighter and more eccentric orbits, similar to those of the observed extrasolar planets on tight orbits (Malmberg, Davies & Heggie, in prep.). During the planet-planet scattering phase, the orbits of planets that ultimately are ejected become progressively wider, producing planets on very wide orbits (see also Scharf & Menou 2009; Veras, Crepp & Ford 2009). Thus, planetary systems resembling the Solar System, which are stable if left alone, may contribute to the population of planets on tight and eccentric orbits, as well as to the population of planets detected on very wide orbits.
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