Aerodynamic properties of fractal grains - Implications for the primordial solar nebula

Gas-grain and grain-grain interactions have a significant role in the evolution of the primordial solar nebula. There is also compelling evidence for larger grains in dense interstellar clouds than in the diffuse interstellar medium. In the usual treatments of grain collisions, where it is assumed that collisions produce compact bodies with a constant density, the gas drag decreases rapidly with size. The first step toward a quantitative analysis of the aerodynamic behavior of fractal aggregates is reported here, and it is shown that for fractals drag decreases very slowly.