More than 500 planets are now known to orbit main-sequence stars in the neighborhood of our Sun, discovered using a variety of detection and characterization techniques. Fifteen years after the first announcement, the formation and evolution of planetary systems is now emerging as a new, quickly expanding interdisciplinary research field. The observational data on extrasolar planets show striking properties indeed, likely evidence of the complexity of the process of planet formation and evolution.

Exoplanets have masses ranging from a few Earth masses up to the 13 Jupiter masses theoretical dividing line between planetary bodies and brown dwarfs. Their orbital periods range from close to one day up to over 15 years, and the eccentricities of their orbits can be as large as 0.95. The increasing number of detections allows one to characterize the statistical properties of extrasolar planetary systems, such as the mass, period, and eccentricity distributions, and the incidence of giant planets as a function of host-star metallicity and mass. These observational data have important implications for the proposed models of formation and early orbital evolution of planetary systems. About 30 multiple-planet systems are known (with up to five components), and as many as 30% of stars with planets might have at least one more planetary mass companion (integrating over all spectral types and for nearby stars within 200 pc). Present-day data on multiple systems provide important clues to the relative importance of several proposed mechanisms of dynamical interactions between forming planets, gaseous/planetesimal disks, and distant companion stars, and allow one to measure the likelihood of formation and survival of terrestrial planets in the Habitable Zones of the parent star. About sixty planets are known to transit across the disk of their primary star, and for these the combination of photometric transit observations (which reveal a planet's radius) and radial-velocity measurements (which permit to determine a planet's mass) provides the only available direct constraint on the density and hence bulk composition of exoplanets. The early evidence for very under-dense and core-dominated transiting planets constitutes the first important challenge to the proposed evolutionary models of the internal structure of strongly irradiated exoplanets, while the first direct measurements of planetary emission and absorption (thanks to observations at various orbital phases with the Spitzer Space Telescope at infrared wavelengths and the Hubble Space Telescope in the visible) have allowed initial comparisons with models of planetary atmospheric chemistry.

When the vaste breadth of exoplanets research is taken as a whole, one then realizes how we're now witnessing the beginning of a new era of comparative planetology, in which our Solar System can finally be put in the broader context of the astrophysics of planetary systems. To this end, help from future data obtained with a variety of techniques will prove invaluable. Planet search surveys, initially focused solely on planet discovery, are now being designed to put the emerging properties of planetary systems on firm statistical grounds and thus thoroughly test the theoretical explanations put forth to explain their existence. Furthermore, both NASA and ESA are now formulating strategies to establish a logical sequence of missions and telescope construction to optimize the pace of exoplanet discoveries (with both direct and indirect techniques) and address key questions on the physical characterization and architecture of planetary systems.

The Symposium brought together leading experts from the many different research disciplines involved with the broad aims of 1) summarizing our current understanding of this rapidly evolving, interdisciplinary research field by discussing the current observational evidence in connection with the most recent theoretical models, and 2) identifying objectives and strategies necessary to advance in the coming years our comprehension of the many processes which connect the formation, architecture, structure, and evolution of planetary systems.