Unconventional planetary orbits and dynamical interactions in stellar clusters

In the last few years the search for planets around main sequence stars other than the Sun has experienced rapid progress but, far from clarifying our knowledge in the field of planet formation, the newly discovered planets have given rise to new uncertainties about our current paradigm for planetary system formation because none of them resemble our own solar system very closely. The unconventional properties of the confirmed extrasolar giant-planets include very small semi-major axes (0.04-0.05 AU) and highly eccentric (0.3-0.7) orbits. We show that some of the unusual features observed in extrasolar planetary systems, which can not be explained by the standard theories, may be a by-product of dynamical interactions between planetary systems and stars in clusters. In this research, the orbital modification problem is studied through the direct numerical integration of entire medium-rich open clusters (N = 1000) with the code NBODY5 (Aarseth 1985). For simplicity, the planetary systems studied in this work consist of only one giant planet and its host star. Our models also include a modern IMF, stellar evolution, and realistic values for the primordial binary fraction. The modification of the primordial orbital elements of planetary systems would be produced through formation of temporarily stable hierarchical systems. On the other hand, unstable configurations can eject one or more planets from the system. In addition, physical collisions between stars and planets with very small semi-major axes and eccentric orbits may result in atypical stellar metallicities.