On the unusual activity of the Perseid meteor shower (1989-96) and the dust trail of comet 109P/Swift-Tuttle

We present the first measurements of the radiant and orbit of meteoroids th at are part of the unusual Perseid activity called the 'Perseid Filament'. This filament was encountered by Earth in the years before and after the re turn of the comet to perihelion in December of 1992. Between 1989 and 1996, there were brief meteor outbursts of near-constant duration with a symmetr ic activity profile. In 1993, however, rates increased more gradually to th e peak. That gradual increase is identified here as a separate dust compone nt, which we call the 'Nodal Blanket'. We find that the Nodal Blanket has a very small radiant dispersion. On the other hand, the Perseid Filament has a radiant that is significantly dispersed and systematically displaced by 0.3 degrees. This dispersion implies that unusually high ejection velocitie s or planetary perturbations must have had time to disperse the stream. In both cases, one would expect a rapid dispersion of matter along the comet o rbit. In order to explain the concentration of dust near the comet position , we propose a novel scenario involving long-term accumulation in combinati on with protection of the region near the comet against close encounters wi th Jupiter due to librations of the comet orbit around the 1:11 mean-motion resonance.