Institute for Advanced Study Informal Astrophysics Seminar

In the early stages of planet formation dust grains collect to form km-sized planetesimals. Growth beyond a few cms is frustrated by collisional shattering and rapid radial drift of pebbles and rocks. I will present my work on the dynamics of pebbles, rocks, and boulders in gaseous protoplanetary disks. The loose drag force coupling with the gas causes particles to pile up in large scale geostrophic gas pressure bumps which arise in turbulence driven by the magnetorotational instability. The local density of rocks and boulders becomes high enough to allow a gravitational contraction into gravitationally bound clusters with masses comparable to solid objects of several hundred kilometers in diameter. I will discuss recent high resolution simulations of this process performed at the Blue Gene/P system at the Juelich Research Center. As 100-km scale protoplanets may form in an environment dense in dust and pebbles, the accretion of small solids is important for their further growth. I show that accretion of pebbles in a gaseous environment leads to prograde spin up of the growing protoplanets, in agreement with the trend for prograde rotation displayed by the largest asteroids.