Abstract

The current era of astronomical observations, Solar System exploration and powerful supercomputers is bringing new insights to the origin of planetary systems. I will focus on the origin of planetesimals, primordial minor planets with sizes ~10 km. These are the least massive gravitationally bound objects in the universe, and their origin is crucial to understanding our Solar System and extrasolar planets. I will describe current ideas for how particle growth crosses the daunting ``meter size barrier” where collisions tend to be destructive and solids can drift rapidly into the host star. I will describe the Steaming Instability, a mechanism that can concentrate pebbles (large dust) to high densities in the disk midplane, triggering planetesimal formation by the gravitational collapse of these pebbles. I will describe how these theories relate to recents observations of protoplanetary disks by ALMA and to the study of the Kuiper belt by telescopes and by the New Horizons mission.