Planetesimal formation near the snow line in MRI-driven turbulent protoplanetary disks

The formation of planetesimals in protoplanetary disks due to collisional sticking of smaller dust aggregates has to face at least two severe obstacles, namely the rapid loss of material due to radial inward drift and particle fragmentation due to destructive collisions. We present a scenario to circumvent these two hurdles. Our dust evolution model involves two main mechanisms. First, we consider a disk with a dead zone. In an almost laminar region close to the midplane, the relative velocities of the turbulent particles are comparatively small, which decreases the probability of destructive particle collisions. Second, turbulence is not the only source of violent relative particle velocities, because high radial drift speeds can also lead to boulder fragmentation. For this reason, we focus additionally on the snow line. Evaporation fronts can be associated with gas pressure maxima in which radial drift basically vanishes. This implies that particle fragmentation becomes even less likely. Our simulation results suggest that particles can overcome the fragmentation barrier. We find that boulders of several 10(2) m can form within only a few thousand years.