The formation of the planets in the solar system is envisioned to occur via a gravitational instability in a thin layer of dust located at the midplane of the primitive solar nebula. The break-up of the dust layer gives rise to seed plants ('planetesimals') that, through successive collisions, eventually form the present-day planets. This thesis addresses the problem of the formation of the dust layer, beginning with a configuration in which the dust particles are uniformly mixed with the nebula's turbulent gas. In the process, four basic ingredients are needed: (1) a model to describe the properties of turbulence in the nebula's gas, (2) a model for the structure of the primitive solar nebula, (3) a formalism to calculate the velocity of dust particles embedded in a turbulent fluid, and (4) a formalism to calculate the space-time evolution of the initial population of dust grains', e.g. mass distribution as a function of time and height above the nebula's midplane, etc. To describe the properties of turbulence in the primitive solar nebula, we use the model by Canuto et al. (1987b) which has been favorably tested against a host of laboratory and astrophysical data. The model of the primitive solar nebula by Cabot et al. (1987a, b), is also used, since it constitutes the most recent and physically plausible investigation of the problem. The available results concerning the calculation of the velocity of particles embedded in a turbulent fluid were found to be unsatisfactory; therefore we developed a new formalism to express the latter quantity in terms of the properties of the turbulence in the fluid. A byproduct of this calculation is a new expression for the coefficient of turbulent diffusion, which should prove useful in future studies. Following the space-time evolution of the grains, we developed a formalism that simulates the simultaneous processes of collisions and sedimentation of the dust grains in the primitive solar nebula. The conclusion of this thesis is that for the model of the primitive solar nebula considered, the formation of a dust layer at midplane is very unlikely. The decay of turbulence seems a necessary condition for the onset of the gravitational instability that is thought to trigger the formation of the planets. (Abstract shortened with permission of author.).
- Pub Date:
- September 1987
- FLUID DYNAMICS;
- Physics: Astronomy and Astrophysics