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Wm. R. Ward (Southwest Research Institute)
The coherent wavelike response of disk systems to perturbations from nearby or embedded gravitating objects is a subject of vigorous study. The internal disk forces accounting for the organized behavior can be either pressure (resulting in acoustic or short waves) or self-gravity (producing gravity or long waves). In addition to their well-known applications to stellar and planetary ring systems, wave phenomena have relevance to protoplanet interactions with their precursor gaseous nebula and with any residual planetesimal disk.
The disk exchanges angular momentum with a perturber via resonant torques. In the absence of collective behavior, only a thin annulus of disk material at each resonance participates in the exchange and can saturate quickly, driving the torque to zero. However, a key trait of waves is their ability to transport angular momentum. Wave action can prevent saturation by transporting angular momentum away from the resonance zone to more distant parts of the disk; this results in a sustained torque that can significantly modify the perturber's orbit.
This talk will review recent changes in the cosmogonic paradigm brought about by ongoing efforts to incorporate disk-planet interactions into models of planetary formation. One dramatic development has been the realization that massive, planet-sized bodies may exhibit a substantial degree of mobility in the presence of their precursor nebula. Not only does this relate to accretion timescales and the provenance of planetary material, but it also has important implications for the origin of close stellar companions and the ultimate survival of planetary systems. Wave action can also manifest itself in the planetesimal disk, even after the dissipation of the nebula. The long-term evolution of residual populations such as the Kuiper and asteroid belts may have been strongly influence by this mechanism. We will outline some of the outstanding problems that have yet to be explored concerning this important topic.
This work is supported by research funds from NASA's Origins of Solar Systems and Planetary Geology and Geophysics programs.