Institute for Advanced Study Informal Astrophysics Seminar

In protostellar accretion disks, magnetorotational turbulence not only transports angular momentum, allowing accretion, but it also strongly influences planet formation. I will consider the influence of turbulence on the formation of planetesimals from boulders, showing that in its presence streaming instabilities can cause direct gravitational collapse of boulders to objects with the mass of dwarf planets, overcoming the meter-size barrier. I will then show that magnetorotational turbulence also forms density enhancements with mass large enough to cause random walk migration of planetesimals, but that dead zones sufficiently neutral to prevent turbulence reduce this effect, without eliminating it. I then consider whether turbulent density fluctuations can pump the ellipticity or inclination of planetesimal orbits. Preliminary results suggest that they cannot do so sufficiently to explain the observed range of orbits in planetary systems, supporting the idea that dynamical interactions after loss of the gas disk are primarily responsible. However, the resulting diffusion of planetesimals outward as well as inward may preserve a significant population from Type I migration into the central star.