A STUDY ON SOLAR DUST RING FORMATION BASED ON FRACTAL DUST MODELS

Using the fractal aggregate model for circumsolar dust grains, the nat ure of the circumsolar just clouds is examined. As a fractal dimension of the aggregate decreases, the porosity of the aggregate increases. Consequently, its temperature becomes independent of its size, and app roaches that of its constituent particles. This evidence suggests that the fractal aggregates with different sizes and made of the same chem ical components sublimate at the same solar distance. This implies tha t the distance of the sublimation zone depends on the chemical composi tion alone. We have found that the aggregates consisting of silicate m aterial, as well as carbon material, sublimate in the solar F-corona. On the other hand, a ratio of radiation pressure force to solar gravit y on the fractal aggregate scarcely increases with decreasing size due to sublimation, in contrast with a strong dependence of its ratio on its size for a compact sphere. Our computer simulation for dynamical e volution of fractal aggregates suggests that they produce a narrow rin g structure in the circumsolar dust cloud, compared with that expected for spherical dust grains. When the aggregates have more fluffy struc ture with a small fractal dimension, however, it is found that the cir cumsolar dust clouds would make no remarkable ring structure.