Turbulence-Assisted Planetary Growth : Hydrodynamical Simulations of Accretion Disks and Planet Formation

• Main Author: Lyra, Wladimir
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för fysik och astronomi 2009
• Subjects: accretion; accretion disks; hydrodynamics; instabilities; methods: numerical; solar system: formation; planets and satellites: formation; magnetohydrodynamics (MHD); turbulence; diffusion; stars: planetary systems: formation; Astronomy and astrophysics; Astronomi och astrofysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9537; http://nbn-resolving.de/urn:isbn:978-91-554-7395-2

The current paradigm in planet formation theory is developed around a hierarquical growth of solid bodies, from interstellar dust grains to rocky planetary cores. A particularly difficult phase in the process is the growth from meter-size boulders to planetary embryos of the size of our Moon or Mars. Objects of this size are expected to drift extremely rapid in a protoplanetary disk, so that they would generally fall into the central star well before larger bodies can form. In this thesis, we used numerical simulations to find a physical mechanism that may retain solids in some parts of protoplanetary disks long enough to allow for the formation of planetary embryos. We found that such accumulation can happen at the borders of so-called dead zones. These dead zones would be regions where the coupling to the ambient magnetic field is weaker and the turbulence is less strong, or maybe even absent in some cases. We show by hydrodynamical simulations that material accumulating between the turbulent active and dead regions would be trapped into vortices to effectively form planetary embryos of Moon to Mars mass. We also show that in disks that already formed a giant planet, solid matter accumulates on the edges of the gap the planet carves, as well as at the stable Lagrangian points. The concentration is strong enough for the solids to clump together and form smaller, rocky planets like Earth. Outside our solar system, some gas giant planets have been detected in the habitable zone of their stars. Their wakes may harbour rocky, Earth-size worlds.