Abstract
For centuries, it was expected that all planetary systems, by virtue of the universality of physical laws, would roughly resemble our own, with small rocky planets on the inside and gas giants on the outside, all on nearly circular, coplanar orbits. However, the discovery of numerous extrasolar planets has revealed the great diversity of planetary systems.
This opening lecture will present the current state of knowledge on the structures of known planetary systems, while placing our own Solar System in this vast context. It will then address the question of how universal laws can give rise to such diversity. This diversity may result from radically different initial conditions, but modern observations of protoplanetary disks reveal that, despite certain variations, these nurseries of planetary formation share many common features. The discussion will then focus on some of the processes involved in planetary formation, distinguishing between those that appear to be deterministic (where small differences in initial conditions lead to small final differences) and those that are more complex and can lead to stochastic behavior (where evolutionary trajectories diverge exponentially, giving radically different results). The realization that planetary formation is highly sensitive to contingencies will lead us to reflect on the likelihood of the existence of planets similar to our own elsewhere in the galaxy, as well as on the possibility of the development of life on exotic worlds.
