APPLICATION of GAS DYNAMICAL FRICTION for PLANETESIMALS. I. EVOLUTION of SINGLE PLANETESIMALS

The growth of small planetesimals into large planetary embryos occurs far before the dispersal of the gas from the protoplanetary disk. The planetesimal-gaseous disk interactions give rise to migration and orbital evolution of the planetesimals/planets. Small planetesimals are dominated by aerodynamic gas drag. Large protoplanets, are dominated by type I migration differential torque. There is an additional mass range of intermediate-mass planetesimals (IMPs), where gravitational interactions with the disk dominate over aerodynamic gas drag, but for which such interactions were typically neglected. Here, we model these interactions using the gas dynamical friction (GDF) approach, previously used to study the disk-planet interactions at the planetary mass range. We find the critical size where GDF dominates over gas drag, and then we study the implications of GDF on single IMPs. We find that planetesimals with small inclinations rapidly become co-planar. Eccentric orbits circularize within a few Myr, provided the the planetesimal mass is large, , and that the initial eccentricity is low, Planetesimals of higher masses, , inspiral on a timescale of a few Myr, leading to an embryonic migration to the inner disk. This can lead to an overabundance of rocky material (in the form of IMPs) in the inner protoplanetary disk () and induce rapid planetary growth. This can explain the origin of super-Earth planets. In addition, GDF damps the velocities of IMPs, thereby cooling the planetesimal disk and affecting its collisional evolution through quenching the effects of viscous stirring by the large bodies.