The eccentricities and inclinations of close-in super-Earths through in-situ giant impacts
Recent observations have found planetary systems composed by multiple close-in super-Earths. These observations have been revealing the distributions of their eccentricities and inclinations. The eccentricities and inclinations would reflect their formation processes. Except the existence of outer perturbers, their eccentricities and inclinations would be the largest if they are formed through in-situ accretion in gas-free environment.
We have investigated evolutions of eccentricities and inclinations of close-in protoplanets in giant impact phase. When close-in super-Earths are formed by in-situ giant impacts, the eccentricities and inclinations of planets are determined by gravitational scattering and collisions. While eccentricities and inclinations are pumped up by scattering, these are damped by collisions even in the gas-free case.
When a collision occurs, the random velocities are cancelled out due to the angular relation of protoplanets. These pumping up and damping processes relax the initial eccentricities. On the other hand, the initial inclinations are not relaxed through giant impacts. This suggests that observed close-in super-Earths, which have nearly coplanar orbits, are initially have small inclinations.