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Project Progress

N. Haghighipour is conducting research focusing on planet formation at its early stage, i.e., from dust grains to km-sized objects. He has previously shown that in a dynamically evolving nebula, where the physical properties of the gas, such as its temperature and pressure, constantly vary, the appearance of gas density-enhanced structures affect the dynamics of small grain in their vicinities. The presence of pressure gradients on both sides of these structures causes solid objects to undergo inward and outward migrations, and accumulate at the location of maximum gas density. During the last year, the analysis was expanded to include the interactions between small dust grains and the background material of the nebula. The results of a recent analysis indicates that, in the vicinity of such structures, dust grains grow to a few centimeters in a short time by sweeping up smaller objects, and rapidly accumulate around the location of maximum gas density on the midplane.

Currently, a new disk model is being developed that includes the gravitational force of the nebula on such moving particles. Existing calculations on the interactions of solids and a nebula do not include the gravitational force of the disk. The gravitational potential of a nebula at its interior points has been calculated, and these results have been applied to nebulae with different gas-density functions. It would be important, particularly for the disk-instability model, to see to what extend the consideration of this force will affect the time of giant planet formation.

Future models will include turbulence in the simulations. It is expected that, once cm-sized particles are accumulated on both sides of the midplane, the velocity differences between solids and gas molecules create turbulence, which inhibits particles coagulation by removing them from the midplane to higher elevations.