1998NewA....4...21D

The discovery of an ejected-planet candidate in a young star cluster in the Taurus Molecular Cloud suggests that ejection of planets is possible in star clusters. Here we consider the possibility that runaway planets are a common occurrence in star clusters. We follow the evolution of several N-body models of star clusters (N ≤ 2500) with a population of mono-planetary systems and calculate the probability of ejection. This probability lies in the range from 0% to 3% with a mean value of about 1.5%, depending on the distribution of semi-major axes of the planetary systems. The results seem to be not dependent of the population of the cluster. Two main processes can contribute to planet ejection in star clusters: dynamical ejection and supernova driven ejection. This work is restricted to the study of the dynamical-ejection mechanism although some conclusions on the supernova mechanism are also pointed out. The mechanism by which these dynamically ejected runaways occur requires the formation of a hierarchical system in the cluster. It has been found that ejected planets have a maximum velocity of ≲ 120 km s^ - 1, and a mass-velocity relation in which the most massive planets tend to have higher velocities. In the light of our calculations, TMR-1C seems to be a clear case of ejection after collision at pericenter of a hierarchical system. We conclude that the spatial density of nomadic planets ejected from star clusters must be very low and that the ejection process from the interaction with stellar neighbors inside the cluster is not dominant. Nomadic planets generated by this mechanism make a very negligible contribution to the overall mass density of the Galaxy.