Formation of Short‐period Terrestrial Planets

We present a model for the formation of non‐resonant multiple short‐period Earths/super‐Earths, based on direct N‐body simulations and population synthesis calculations. We investigated the distributions of mass, semimajor axis and orbital eccentricities of solid planets; in particular, those of rocky planets in inner disk regions, in the absence of effects of gas giant planets. In the inner regions, embryos accrete most of the planetesimals by disk gas depletion. Coupled effects of Type I migration of embryos, termination of the migration near the inner disk edge, and resonant trapping between embryos all produce a resonantly trapped cluster of embryos that extends from the disk inner edge of ∼0.04 AU to beyond 0.1 AU. After tidal eccentricity damping due to the gas disk declines, the embryos undergo orbit crossing and their eccentricities are pumped up through close scattering between them. They collide with each other (giant impacts) to increase mass by an order of magnitude over 100 Myr. They form multiple Earths or super‐Earths in non‐resonant orbits around ∼0.1 AU with moderate eccentricities of 0.01–0.1 in the disks with masses comparable to or a few times larger than the minimum‐mass solar nebula model. If the disk‐star magnetic coupling is weaker than a critical value, the short‐period multiple Earths or super‐Earths would be engulfed by their host stars and the inner regions at ≲1 AU would become clear. The variation of strength of the disk‐star magnetic coupling may produce a diversity of distributions of short‐period terrestrial planets.