Signatures of hit and run collisions

Terrestrial planets grew in a series of similar-sized collisions that swept up most of the next-largest bodies. Theia was accreted by the Earth to form the Moon according to the theory. Planetesimals likewise may have finished their accretion in a sequence of 'junior giant impacts', scaled down in size and velocity. This chapter considers the complicated physics of pairwise accretion, as planetesimals grow to planetary scales, and considers how the inefficiency of that process influences the origin of planetesimals and the diversity of meteorites and primary asteroids.