Most stars form in some sort of stellar cluster or association. In such environments the number density of stars is much higher than in the solar neighbourhood, which means that close encounters between stars may be relatively common. Using numerical simulations we quantify the fraction of single stars in the solar neighbourhood that have never suffered a close encounter or been part of a binary system. We call such stars singletons. Furthermore, we study what would happen to a solar-system-like planetary system if its host star was exchanged into a binary system during an exchange encounter in a young stellar cluster. The perturbation of the companion star might in such a system trigger strong planet-planet scatterings. This would subsequently lead to the ejection of one or more planets, leaving those remaining on tighter and more eccentric orbits. We find that only if the gas giants in solar-system-like planetary systems most often have rather similar masses does the resulting eccentricity distribution resemble that of the observed extrasolar planets.
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