N-Body Simulations of Multiplanetary Systems in Star Clusters: The Effect of External Perturbations on the Dynamical Evolution of Planets

Stars predominantly form in groups or clusters, which, however, only dissolve completely after hundreds of millions of years. Within such stellar overdensities, stars interact gravitationally with each other. On timescales of the order of millions of years, close flybys of neighbouring stars occur, which can significantly alter the orbital architecture of the planetary systems that have formed around the stars in the cluster. In this thesis, I simulate a total of four star cluster environments of different densities and subsequently numerically integrate different planetary system architectures over 100 million years, taking into account the gravitational forces that would have acted on them due to the motion of their central stars through the cluster. The results show that the gravitational perturbations from the birth environment can explain the large diversity in the orbital parameters of the observed exoplanet population. In particular, the simulation results show that about 1–2% of all planets adopt stable retrograde orbits due to external stellar perturbations or resulting interactions with other planets in the system. Furthermore, by taking into account tidal interactions between the host star and the planets, the formation of hot Jupiters can be observed in some systems as an indirect consequence of stellar encounters. Moreover, all simulated star cluster environments produce a significant percentage of unbound planets