DIFFERENTIAL ROTATION AS A SOURCE OF ANGULAR-MOMENTUM TRANSFER IN THE SOLAR NEBULA

We show why differential rotation is the most natural source of the turbulence in the solar nebula. Turbulence is likely to occur via localized, small but not infinitesimal perturbations of the Keplerian shear. Such perturbations occur naturally via pressure fluctuations, interactions with planetesimals, or material infall. Some conditions necessary for such perturbations to destabilize the basic flow are derived and shown to be satisfied by the solar nebula. The characteristics of such a shear-driven turbulence are discussed, with reference to current atmospheric observations, laboratory experiments, and numerical simulations. Its efficiency can be computed and translated into an α parameter (turbulent viscosity in units of the speed of sound, and the orbital time scale) of the order of 2 × 10-3. The implications of such results for the solar nebular are discussed, with emphasis on its structure and evolution. A high-mass solar nebular (0.3 M⊙) in which angular momentum is transferred only via differential rotation evolves in a time scale consistent with that indicated by current observations. © 1993 Academic Press. All rights reserved.