Protostars and Planets VI, Heidelberg, July 15-20, 2013
Sweep-up growth at the inner edge of dead zones
Drazkowska, Joanna (Heidelberg University, Center for Astronomy, Institute for Theoretical Astrophysics)
Windmark, Fredrik (Heidelberg University, Center for Astronomy, Institute for Theoretical Astrophysics)
Dullemond, Cornelis P. (Heidelberg University, Center for Astronomy, Institute for Theoretical Astrophysics)
Planetesimal formation is still not understood. Coagulation models have revealed numerous obstacles to the dust growth. One of them is the bouncing barrier. The growth of small dust grains was shown to be completely halted already for cm-sized silicate particles. This barrier can be actually beneficial to the growth. When a limited number of grains is inserted into a population halted by the bouncing, growth to planetesimal sizes is possible. This is because as long as a collision between two big particles generally leads to fragmentation, a collision involving non-equal sized aggregates can lead to growth via so-called fragmentation with mass transfer. The origin of the first seeds is a problem for this scenario.
We propose a new method of providing the seeds. We find that a steep radial variation in the turbulence efficiency that takes place at the inner edge of a dead zone, promotes planetesimal formation via sweep-up in several ways. It provides a pressure trap that saves the dust from the radial drift barrier. It also causes a change in the maximum size of aggregates at which growth barriers occur. The seeds can grow in the dead zone, where the bouncing barrier occurs for larger grains, and then be delivered by radial mixing to the MRI active region, where the growth via sweep-up occurs. In the presented model, which is employing an ad hoc turbulent viscosity change near the snow line, it is possible to grow planetesimals by incremental growth on timescales relevant for planet formation.
Click here to view poster PDF