An international group of astronomers, led by Martin Schlecker of the Max Planck Institute for Astronomy, has found that the arrangement of rocky, gaseous and icy planets in planetary systems is apparently not random and depends on only a few initial conditions. The study is based on a new simulation that tracks the evolution of planetary systems over several billion years. Planetary systems with Sun-like stars, which produce in their inner regions super-Earths with low water and gas content, very often produce a planet comparable to our Jupiter on an outer orbit. Such planets help to keep potentially dangerous objects away from the inner regions.