Planetary systems

We provide a non-technical introduction to some current topics in planetary system origins, relevant to the understanding of a decade's worth of discovery and characterization of systems other than the solar system. We consider both the radial velocity exoplanets (planets outside the solar system) and the dust disks known as transitional and debris disks, which are natural and conspicuous parts of young planetary systems. Our emphasis is on new dynamical theories, including new concepts in disk-planet interaction and the resultant three types of migration of protoplanets in disks. Migration is considered the key issue for planet survival during the T Tauro disk phase. We also discuss a variety of observable features arising from the dust-gas coupling in the presence of stellar radiation pressure. Nonaxisymmetric features have been both observed and predicted theoretically, although detailed comparison has not yet been performed.