Dust evolution in protoplanetary disks: planetesimal formation and dust ring formation
Planet formation starts with the growth of micron-sized dust grains in a protoplanetary disk into kilometer-sized planetesimals. The physics of grain sticking is highly complex and has been extensively studied by recent laboratory and numerical collision experiments. In this talk, I will review the key results of these recent collision experiments with an emphasis on how the sticking efficiency of dust aggregates depends on their compositions and internal structure. I will then introduce our latest work on the modeling of multiple dust rings around HL Tau. The latest ALMA observation of HL Tau revealed spectacular concentric dust rings in its circumstellar disk. We attempt to explain this multiple ring structure as a consequence of aggregate sintering. Sintering is the process of making a particle aggregate brittle and occurs at temperatures slightly below the melting point. I will show that sintering induces fragmentation and concentration of icy dust aggregates in the vicinity of the snow lines of various volatiles. The multiple dust rings produced in this way share many similarities with those of HL Tau.