Planetary Science Seminar

 It has long been difficult to understand how dust grains could grow past the "meter-size barrier" to become super-km scale planetesimals, the solid building blocks of planets.  Daunting obstacles include the  rapid radial drift of solids towards the star and the tendency of many collisions to result in destruction or bouncing instead of growth.  The route to planetesimals focuses on two broad mechanisms.  First finding the circumstances that may lead to more effective collisional growth towards or even beyond the meter-size barrier.  Second, (aero)dynamical mechanisms to concentrate smaller solids into gravitationally bound planetesimals.  The classic dynamical mechanism is a gravitational instability of the particle disk.  In the streaming instability mechanism, drag forces and radial drift can automatically produce strong particle clumps.  Recent simulations have explored the viability of the streaming instability across a broad range of parameter space.  I will asses the viability of the streaming instability and other planetesimal formation mechanisms, including a discussion of the large scale dust structures observed in protoplanetary disks.