Toward a Deterministic Model of Planetary Formation V. Accumulation Near the Ice Line and Emergence of Short-Period Earths

We address two outstanding issues in the sequential accretion scenario for gas giant planet formation, the retention of dust grains in the presence of gas drag and that of cores despite type I migration. Theoretical models suggest that planets form in protostellar disk regions with an inactive neutral “dead zone” near the mid plane, sandwiched together by partially ionized surface layers where magnetorotational instability is active. Due to a transition in the abundance of dust grains, the active layer’s thickness decreases abruptly near the ice line, which leads to local surface density and pressure distribution maxima near the ice line. This barrier locally retains protoplanetary cores and enhances the heavy element surface density to the critical value needed to initiate efficient gas accretion. We simulate and reproduce the observed frequency and mass-period distribution of gas giants around solar type stars without having to greatly reduce the type I migration strength. We also predict slightly smaller populations of Earth-mass planets in the habitable zone and close to their host stars. Subject headings: planetary systems: formation – solar system: formation – stars: statics