The Importance of Collisional Fragmentation in Terrestrial Planet Evolution

Collisional fragmentation was an important process in the early solar system that greatly affected the formation of the terrestrial planets. After the dispersion of the circumsolar gas disk, gravitational interactions between planetesimals and growing planetary embryos dominated the terrestrial accretion environment. Collisions between these massive bodies likely accounted for the final accumulation of mass into the present-day solar system. Debris from these collisions has been shown to prolong the period of terrestrial planet growth and significantly damp the orbits of the young planets. The inclusion of collisional fragmentation is critical to models of terrestrial planet accretion and to our understanding of the formation and evolution of the inner solar system. Swiftest SyMBA is a powerful new symplectic integrator developed by the Purdue Swiftest team. Building off the legacy of Swift and Swifter, Swiftest SyMBA is a multiple time step mixed variable symplectic (MVS) integrator capable of resolving close encounters between massive bodies. In previous versions of the SyMBA integrator, when a close encounter is determined to result in a collision, all of the mass of the colliding bodies is perfectly conserved in a single resultant body. Our new Swiftest SyMBA goes a step further to resolve the outcome of the collision, including multiple fragmentation regimes and the production of collisional debris. The inclusion of collisional regime determination in the SyMBA integrator makes Swiftest SyMBA a modern and accurate tool for modeling the formation and evolution of gravitationally dominated systems. To demonstrate the capabilities of Swiftest SyMBA, and to stress the importance of collisional fragmentation, we explore 8 unique models of terrestrial planet accretion. The results of these models show that collisional fragmentation not only prolongs the accretion period of the terrestrial planets, but also changes the size distribution of bodies in the proto-planetary disk. Understanding the size-frequency distribution of these bodies could lead to a better understanding of early solar system impactor populations, including early martian impactors.