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H. Klahr (MPI fuer Astronomie), P. Bodenheimer (UCO/Lick Observatory)
Neither one of the classical formation scenarios for giant planets seems sufficient. The disk instability model has problems in explaining the low disk temperatures needed for its operation, and the core accretion model has too long a time scale unless solid surface densities in a disk are rather high. We suggest a new scenario that combines the virtues of both models. Vortices may play a crucial role in the formation of planets. They are probably formed naturally in protoplanetary accretion disks from a so-called Global Baroclinic Instability that arises if the radial entropy gradient is strong enough. The vortices show up as huge stable anti-cyclonic rotating gas masses, that can be regarded as planetary precursors for two reasons. First they produce peaks in the gas surface density about four times higher than in the ambient medium, and second they concentrate very efficiently all solid particles above a certain size in their center. Thus vortices are preferred formation sites for planets. A three-stage formation scenario can be invoked: (1) formation of stable vortices, (2) concentration of solid particles in the vortex and formation of a planetary core, and (3) accretion of gas onto the core. Using ALMA it will be possible to do direct imaging of vortices. In addition we suggest that the eclipses of the object KH15D could be produced by a large vortex in the inner part of a circumstellar disk.
This work was suported by the NASA grant NAG5-4610 and by a special NASA astrophysics theory program which supports a joint Center for Star Formation Studies at NASA-Ames Research Center, UC Berkeley, and UC Santa Cruz.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.