Inhomogeneities in protoplanetary disks and the population of exoplanetary systems
The large number of recent high-resolution observations shows that protoplanetary disks have a various kind of “structures” in their properties. For example, SMA observations infer a radial discontinuous structure in the gas-phase CO column density. It is well recognized that this kind of structures, or “inhomogeneities”, in disks are the consequence of the mixture of a number of physical and chemical processes taking place in the disks. Here, we present a very comprehensive study of disk inhomogeneities in which we investigate how the disk inhomogeneities affect planet formation that proceeds in the disks. We demonstrate that disk inhomogeneities give rise to planet traps – specific sites in protoplanetary disks at which rapid type I migration is halted. We show that up to three types of traps (heat transitions, ice lines and dead zones) can exist in a single disk, and that they capture planetary cores and transport the cores from large to small orbital periods very slowly, as the disk accretion rate decreases with time. We also demonstrate that planetary populations, that are generated by the combination of the standard core accretion scenario with planet traps, are consistent well with the observations of exoplanets, wherein most gas giants are piled up around 1 AU with a large number of low-mass planets in tight orbits. We finally discuss the observational disk properties that can arise from disk inhomogeneities. It is important that such disk properties may be examined by ALMA observations.