Observational Planet Formation I: Introducing the New Field
Ruobing Dong

Nearly every single Sun-like star in our galaxy hosts a planetary system. How planets form in gaseous protoplanetary disks surrounding newborn stars is among the most exciting and fastest growing fields in all of astrophysics. The best way to learn how planets form from observations, is to directly watch them forming in disks. By definition, this is the most direct way for us to quantitatively constrain the timescale, the location, the local environment, and the statistics of planet formation. In the past, due to the difficulties in detecting planets forming in disks, planet formation was largely a subject of theoretical astrophysics. Now, thanks to a fleet of new instruments with unprecedented resolving power that have come online in the past few years, we have just started to unveil structures in resolve images of protoplanetary disks, such as gaps and spiral arms, that are most likely induced by embedded (unseen) planets. By comparing observations with theoretical models of planet-disk interactions, the locations and masses of these still forming planets can be constrained. This marks the beginning of a brand new field -- observational planet formation.