Colliding in the Shadows of Giants: Planetesimal Collisions during the Growth and Migration of Gas Giants

Giant planet migration is an important phenomenon in the evolution of planetary systems. Recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal-planetesimal collisions, during gas giant growth and migration. The numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. We find that giant planet growth alone has little effect on impact velocities, and most of the planetesimals scattered by growing giants do not undergo collisions with each other during the growth period. In contrast, we find that giant planet migration induces large numbers of high velocity collisions between planetesimals. These impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals, and to cause catastrophic disruption of the bodies. New bodies may form from impact debris. Collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt via giant planet growth and migration. A small fraction of the largest planetesimals implanted into the asteroid belt would have been processed via collisions. We identify important consequences of planetesimal collisions that have not been considered in planet accretion models. The prevalence of high velocity collisions during giant planet migration, and their potential links to the properties of meteorites, and the formation of chondrules, makes impact vaporization a critically important phenomenon. The consequences of vaporizing planetesimal constituents require further detailed study. New collision outcome models for impacts within the nebula, and models for new planetesimal formation are needed.