Talk Title: Challenges in computational planet formation; from disk instability to planetesimal formation.
Abstract: I will discuss recent progress in modeling a number of important regimes in planet formation. First I will report on recent developments in the disk instability model for giant planet formation, which is attractive to explain extrasolar gas giants on wide orbits. I will show how new Lagrangian hydrodynamical techniques can solve the long standing issue of non-convergence of the critical cooling for disk fragmentation. The same hydro method allows to study the combination of self-gravity and MHD turbulence in disks, offering the intriguing possibility that angular momentum dissipation by MRI may promote gravitational instability. I will then discuss planetesimal formation scenarios, introducing a new drag-vorticity instability whereby vortices in disks can generate long-lived, large enhancements of dust density which could be the precursors of planetesimals. This scenario is alternative to the conventional streaming instability and can take place starting from a wider range of initial properties of the dust layer. Finally, with the help of a novel sub-grid model for the coagulation and fragmentation of dust grains implemented in our multi-fluid code, we show how the common practice of simulating only single grain sizes can lead to incorrect results for the transport of dust through the disk.