The focus of this project is the study the mechanisms responsible for driving turbulence in protoplanetary disks, and the effect of such turbulence on two critical stages of the planet formation process - the motion of dust within the disk and the early growth of kilometer-scale bodies called planetesimals. Here, Dr. Armitage and a postdoctoral scholar will develop new global simulations of protoplanetary disks that will be used to study two important sources of turbulence: that driven by the magnetorotational instability and that generated by the self-gravity of the disk gas. The simulations will improve upon prior work both by attaining higher resolution, and by more accurately reproducing the physical conditions likely to exist in young protoplanetary disks. Using the simulations, they will determine how efficiently dust diffuses within the turbulence, and in particular whether the large-scale structure of the turbulent disk enhances the transport as compared to local models. They will also calculate the equilibrium velocity dispersion of bodies within the disk, whose orbits are excited by gravitational scattering off turbulent fluctuations and damped by gas drag. From this, they will determine the prerequisites for planetesimals to grow rather than suffer destructive collisions. The results are expected to elucidate where in the disk planet formation can occur, and whether significant steps toward growth can occur in the earliest phases of disk evolution when the disk is massive and turbulent.
This project will directly contribute to the professional training of a junior scientist. Also, during the grant period, Dr. Armitage will complete and publish a graduate level textbook entitled "Astrophysics of Planet Formation," which will cover topics directly relevant to this project and which will incorporate results of this research. At the undergraduate level, Dr. Armitage will integrate selected aspects of this work into a class for non-science majors on "Extraterrestrial Life," make course materials available electronically, and continue his participation in NSF-supported experiments into new techniques for teaching science. For the general public, he will revise an existing planetarium show on extra-solar planets, both to incorporate new results and to take advantage of improved digital technology at the University of Colorado's Fiske Planetarium. The technical results of the investigation will be disseminated widely via journal articles that are freely via the arXiv preprint server.
