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

Abstract

We present the first measurements of the radiant and orbit of meteoroids that are part of the unusual Perseid activity called the ‘Perseid Filament’. This filament was encountered by Earth in the years before and after the return of the comet to perihelion in December of 1992. Between 1989 and 1996, there were brief meteor outbursts of near‐constant duration with a symmetric activity profile. In 1993, however, rates increased more gradually to the peak. That gradual increase is identified here as a separate dust component, 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°. This dispersion implies that unusually high ejection velocities 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 orbit. In order to explain the concentration of dust near the comet position, we propose a novel scenario involving long‐term accumulation in combination with protection of the region near the comet against close encounters with Jupiter due to librations of the comet orbit around the 1:11 mean‐motion resonance.

On the dynamics of meteoroid streams

“…The +3 magnitude visually observed meteoroids should have 1.8 times broader profile than the -1 magnitude photographic meteoroids. Although the observed alpha Monocerotid flux profiles are not inconsistent with the expected larger dispersion for smaller particles (Jenniskens et al, 1997a), the Perseid outbursts do not confirm the expected behavior (Jenniskens et al, 1998).…”

“…Also, Perseid outbursts were detected prior to the comet, but with the Earth inside of the comet orbit. In this case, the observed activity behavior before and after the comet is almost symmetric, with the peak activity decreasing by a factor of 10 over a period of 2.8 years in front of, and 4.4 years behind the comet (Jenniskens et al, 1998).…”

“…Examples of radiant distributions for the Perseid, Leonid and alpha-Monocerotid outbursts are shown in Figs. 2-4 (Jenniskens et al, 1997a(Jenniskens et al, , 1998Betlem et al, 1997). For the first time, we can now distinguish between the dispersion in right ascension and that in declination.…”

“…Figure 2 compares the radiant positions of the precisely reduced orbits of meteoroids obtained during the Perseid outbursts in 1993 and 1994 with the much larger dispersion measured for the annual Perseids by the same technique (Jenniskens et al, 1998). The annual Perseid shower is a strong shower and must have contributed many, if not all, of the outlayers in the radiant distribution of 1993/94.…”

“…The comet returned to perihelion in December of 1992. Between 1989 and the present, a brief increase of rates was observed with a characteristic duration (Jenniskens et al, 1998). Visual observations of Perseid outbursts from around the globe have been summarized by Brown and Rendtel (1996), while radar observations are given by Simek and Pecina (1996).…”