Alternative Planet Formation Scenarios

Robert L. Kurucz (CFA)

FU Orionis events:
I have worked out processes that conserve angular momentum by ejecting protostellar material at the equator to balance infall at high latitudes during an FU Ori event. Excess infall blocks convective downflow but not convective upflow. The convective upflow produces meridional flow toward the equator. Stellar material inside the dipole torus that connects the star to the disk flows outward carrying angular momentum to make an oblate supergiant-type envelope that is not strongly coupled to the star. When the infall drops back to normal levels, the oblate envelope is slowly evaporated by strong UV and X radiation from the protostar. Some matter flows or blows into the inner wall of the disk.

Magnetically-driven planet formation:
If the dipole field pulls out of the disk during an FU Ori event, the field wraps and tangles around the extended envelope. Reconnections compress the trapped plasma into an unstable magnetic torus orbiting the star (a tokamak). The torus reconnects into self-gravitating magnetic spheroids (spheromaks) that become planetary cores. The reconnection radiation and winds heat and compress the disk causing agglomeration out to the snow line. The cores grow by collecting material infalling toward the star. They are in unstable orbits that can change radically or they can be ejected from the system. A core in a highly eccentric orbit that goes far into the disk can become very massive because it sweeps up material over a wide range of radii.

Radiatively-driven planet formation:
If the dipole field pulls out of the disk when the protostar is not in an Fu Ori phase, the field wraps and tangles but there is no large reservoir of plasma to compress. The reconnections fill 75% of the surface of the star with CMEs and flares. The reconnection radiation and winds heat and compress the disk causing agglomeration out to the snow line. The agglomerated material rapidly forms planetesimals and inner planets.

Classical planet formation:
Outer disks form planets by slow uniformitarian processes.