Striated dust tail of Comet West 1976 VI as a particle fragmentation phenomenon

The motions of 16 striae in the dust tail of Comet West between 4 and 7 March 1976 have been successfully fitted on four small-scale photographs. Our model assumes that the striae are the result of the ejection of dust particles that subsequently fragment in the tail. The particles responsible for the formation of a discrete stria must be emitted simultaneously, be subjected to the same repulsive acceleration in the tail, and break up simultaneously. The results of the analysis indicate a strong correlation between the ejection times and the times of known explosive events. The repulsive accelerations of the fragments are found to be between 0.6 and 2.7 times the solar attraction, indicating submicron-sized absorbing particles. We also find that the repulsive accelerations of parent particles are only slightly smaller than those of their fragments, suggesting comparable area-to-mass ratios between parents and fragments, and therefore highly nonspherical shapes of parents. Complex, tenuously bonded, chain-like aggregates of submicron-sized grains would satisfy these conditions. The mass of dust in an average stria is estimated to be about 109 g. There was no measurable effect from the Lorentz force, indicating an upper limit of a few volts for the electric charge of the fragments. We consider rotational bursting caused by a ''windmill'' effect of radiation pressure to be a possible fragmentation mechanism. Application of a simple chain-particle model suggests the existence of discrete particle types