Turbulence in the solar nebula and formation of the outer solar system

Turbulence is a major physical process of the solar system formation. However, its direct numerical simulation by available computers remains impossible, due to the dramatic range of dynamical scales in the flow. To circumvent this difficulty, a model enabling an effective reduction of the degrees of freedom of the problem is actually used. For accretion disks it is classically done by calculating only the mean quantities of the flow and parameterizing the fluctuations with a turbulent viscosity. We have used this approach to isolate the main physical processes governing the whole process of planetary formation. By using the constraint relying in the D/H fractionation between water and hydrogen, we have precisely defined the thermodynamical properties of the solar nebula in which comets and giant planets formed. Especially, we have been able to interpret current observational data on giant planets composition. However, the outer solar system bodies exhibit a large variety in their compositions which seems closely related to turbulent fluctuations in the solar nebula. Since fluctuations are explicitly excluded from the standard approach, it seems necessary to develop a new model in which they are calculated. The theoretical basis of such model has been defined and applied to the simplest shear flow: the plane Couette flow. (author)