Lecturer: Mr. Evgeni Grishin Affiliation: Technion - Israel Institute of Technology Abstract: The growth of small planetesimals into large planetary embryos occurs much before the dispersal of the gas from the protoplanetary disk. The planetesimal - disk interactions cause migration and orbital evolution of the planetesimals/planets. Small planetesimals are dominated by aerodynamic gas drag. Large protoplanets, >1000km in size, are dominated by type I migration torque. There is an additional size range, 200- 1000 km, 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 and study the implications of GDF on single IMPs. We find that planetesimals with small inclinations and eccentricities circularize rapidly. Planetesimals of higher masses inspiral on a few Myrs time-scale, which leads to an over-abundance of rocky material in the inner protoplanetary disk (<1 AU) 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. In addition, Solar System observations indicate that binary planetesimals (BPs) are common. We find that the GDF can induce BP mergers on a few Myrs time-scale, which affect the structure of merger-formed planetesimals. Taking GDF into account is important for the evolution of the planetesimal disk. In addition, BPs on eccentric orbits evolve in the supersonic regime, where they exhibit considerable softening that enhance the cross section for planetesimal encounters and affect planet formation. Additional details of the upcoming Astrophysics' seminars can be found on the following link. ‏האירוע הזה כולל שיחת וידאו ב-Google Hangouts. הצטרף: https://hangouts.google.com/hangouts/_/mail.huji.ac.il/astrophysics?hceid=bWFpbC5odWppLmFjLmlsX2c0czhydDlpcmhwZzRvdGNybWIzZGFqcjdvQGdyb3VwLmNhbGVuZGFyLmdvb2dsZS5jb20.638er027k1gsfd9q73v9aqdias&hs=121