Collisions between protoplanets: data analysis and classification

Abstract

Abstract Collisions between protoplanets are common events in the later stage of the planetary formation process. Protoplanets grew into present-day planets through these collisional events. It is therefore necessary to obtain information about redistribution of mass and angular momentum between colliding two bodies in order to study the growth rates of planets and the origin of their spin. We have started a series of systematic studies on this theme, and this is our first report. Here, we concentrate on the impact between one protoplanet, which has one Earth mass, and another protoplanet with 0.06 Earth mass. The motion of two bodies are pursued numerically by the SPH simulation method. We change the minimum distance between the two bodies as the variable parameter to specify their orbital angular momentum. For each value of the parameter, we repeat the numerical simulations and obtain final states of bodies. Such various final states are examined by criteria developed to distinguish some clusters formed by many SPH particles. We determine instantaneous orbital elements for relative motion between central protoplanet and each cluster. From this information, we forecast the destiny of each cluster, for example, to be merged into the target body or trapped. Then we determine the initial conditions that result in final characteristic states. The 5 states are the merging state in which the impactor is absorbed to the target, the multiple impact state in which the impactor collides with the target again and again, the disruption escaping state in which the impactor is tidally disrupted and a large part of the impactor escapes from the target, the trapping state in which the impactor is trapped by the target, and the passing state in which the impactor passes through as it is.