Millimeter-Radio Observations of the Hallmarks of Planet Formation in Circumstellar Disks

Some of the fundamental processes involved in the assembly of planetary systems are just now becoming accessible to astronomical observations of circumstellar disks. The new promise of observational work in the field of planet formation makes for a very dynamic research scenario, which is certain to be amplified in the coming years as the revolutionary ALMA facility ramps up to full operations. To highlight some of the new directions being explored in this field, I will describe how we are using high angular resolution measurements at mm radio wavelengths to study two crucial aspects of the formation and early evolution of planetary systems: (1) the growth and migration of disk solids, and (2) the interactions between a young planetary system and its natal, gas-rich disk. For the former, I will demonstrate that we have identified evidence for spatial variations in both the particle size distribution and (potentially) the gas:dust mass ratio in young disks, and how those could translate into new constraints on models of grain growth and radial drift. And for the latter, I will review what we have learned from directly resolved radio observations of large, dust-depleted cavities in the centers of so-called "transition" disks, including their surprisingly high frequency and some possibilities for the observational study of planet-disk interactions.