Comet Halley meteor stream: a new model

Although the association of the Orionid and η-Aquarid meteor showers with Comet Halley has long been recognized, a satisfactory explanation of the displacement of the meteoroid streams from the comet orbit has not been given. Analysis of observations of the showers, comprising all larger series of data since the beginning of this century, led to structural features scarcely explained by the previous toroidal model of the stream. All these features (width of both showers, activity levels, activity variation, shifts in activity maxima) are more satisfactorily explained by the new shell model of the stream. Our present work utilizes the recently determined history of the comet orbit back to 1404 BC. Perturbations by the major planets produce rapid motion of the longitude of the nodes (Ω) of the comet orbit. We postulate that the meteoroids simply exist in orbits where the comet was many revolutions ago. Because of the large range of possible values of $$\Delta\Omega$$, 0°–2°, a pseudo-diffusion process has distributed the meteoroids over the shell-like surface traced out by the long-term evolution of the comet. Accepting the calculations of Kozai which indicate that the argument of perihelion of Comet Halley librates, we calculate that the shell is confined to a strip which subtends an angle of 25° at the major axis. Concomitant with the spreading of particles over the shell, perturbations parallel to the orbital plane cause thickening into a belt. The observational data on the showers suggest a superposition of several belts which correspond to the stable zones of increased shower activity. The cross-section of the belt at the Earth's orbit is 0.44 AU perpendicular to the orbital plane and about 0.05 AU in the plane.