Oral Presentation

The crucial role of magnetic fields in top-down planet formation

Author(s): Hongping Deng (Shanghai Astronomical Observatory)

Presenter: Hongping Deng (Shanghai Astronomical Observatory)

Protoplanetary discs as young as 0.5 Myr bear gaps and rings, arguable signposts of protoplanets. In the early stages, the disk is unstable due to gas self-gravity and spiral density waves feature. In unprecedentedly high-resolution simulations (up to 72M particles), we show that spirals can drive large-scale vertical circulations and amplify any seed magnetic fields to nearly thermal amplitudes. This dynamo is vigorous even in poorly ionized regions of the protoplanetary disk. If the spiral collapses due to efficient cooling, the magnetic fields will wrap up the fragment and effectively isolate the fragment from the turbulent disk. We found fragments as light as Neptune survive in disks thanks to the protection of magnetic fields. They may later capture solids in their cores, and thus a rapid top-down formation is possible for major types of planets. Preliminary results with an advanced radiative transfer scheme will also be presented.