Simulation Experiments on Dust Aggregation in the Early Solar Nebula

Details Simulation Experiments on Dust Aggregation in the Early Solar Nebula Simulation Experiments on Dust Aggregation in the Early Solar Nebula

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.1102w&link_type=abstract

American Astronomical Society, DPS meeting #28, #11.02; Bulletin of the American Astronomical Society, Vol. 28, p.1107

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Scientific paper

The evolution of dust particles in the early solar nebula is most probably determined by aggregation of micron-sized grains. With respect to different scenarios as Brownian motion, differential sedimentation, orbital decay and turbulence, relative velocities between different particles are generated which lead to subsequent collisions, sticking and growth. The aggregates evolve to certain structures which might be characterized by a fractal dimension d, relating the mass m of the clusters to its size s, m ~ s(d) . Computer simulations show that d is supposed to be close to 2. The value of d is important for the timescales of the formation of planetesimals. Parameters for the model calculations, such as sticking probabilities for different velocities and the ability of the particles for sliding and rolling on the surfaces during impacts are needed. We carried out collision experiments with aggregates consisting of up to a few hundred single micron-sized amorphous SiO_2 particles. The device generating these aggregates, an aggregation experiment of its own, produces clusters of the fractal dimension 1.9. In 'levitation tube' experiments, we observed collisions between single clusters due to differential sedimentation. The collision velocities ranged from 1 mm/s to 1 cm/s. All collisions resulted in sticking as predicted by theory. We found no significant restructuring within the limits of our optical system, a long distance microscope and flash lamp illumination. Images were taken by a digital CCD camera (256 * 256 pixels) with 150 frames per second. In another series of experiments under the microgravity conditions of the drop tower in Bremen as well as in the laboratory, we directed a beam of the above-mentioned clusters to a thin target and observed sticking and restructuring due to the impact and gravitational torques. We will present new results of these investigations.

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