Astron. Astrophys. 324, 770-777 (1997)

1. Introduction

Short-period comets (hereafter SPC) are one of the most likely sources of interplanetary dust. To estimate their actual contribution to the dust mass in the zodiacal cloud, we have to know the dust production rate and the fraction of grains injected in bound orbits. The average dust production rate of SPC was assumed to be about 10⁵ r^-2 g s^-1, where r is the Sun-comet distance in AU (Mukai 1989), but it can vary significantly among SPC. The orbital evolution of cometary dust particles depends on the starting orbital parameters related to the ejection velocity, on solar gravitational, radiation and corpuscular forces and on gravitational perturbations by planets. In this paper we discuss the orbital evolution of the dust emitted by two short period comets characterized by very different orbits, namely P/Schwassmann-Wachmann 1 (P/SW1) and P/Griegg-Skjellerup (P/GS). P/SW1 is a trans-Jupiter object, so that all the dust released from this comets is heavily perturbed by Jupiter during its orbital collapse towards the inner Solar System. On the other hand, P/GS aphelium does not reach the Jupiter Sun distance, so that the orbital evolution of the dust released from this comet should be more sensitive to radiation drag effects than P/SW1 meteoroids.

Both comets have been analyzed by means of the inverse numerical model of comet dust tails and outer comae developed by Fulle (1989), which gives information on the dust size (diameter) distribution, production rate, emission anisotropy and velocity. P/GS has been the second target of the GIOTTO mission and there have been efforts to get ground-based observations at the same time of the probe fly-by. In this way it was possible, by applying the quoted tail model, to compare ground-based results with in-situ dust measurements (McDonnell et al. 1992), performing a check of the model and giving more reliability to the parameters of the dust particles. The main output of both approaches was that P/GS, as P/Halley, produces dust with its mass lying all in the largest grains, with a perihelion mass loss rate of 200 kg s^-1 and a dust ejection velocity of 15 m s^-1 for grains with a diameter of 0.15 mm (Fulle, et al., 1993), so that this minor short-period comet too might be a significant zodiacal dust source.

The P/SW1 tail modeling was devoted to estimate the possible meteoroid supply from trans-Jupiter sources (Fulle, 1992). A surprising tail model output was the high P/SW1 dust mass loss rate, larger than 300  kg  s^-1, ten times larger than the value suggested by early coma observations (Jewitt 1990), interpreted assuming unrealistic dust velocities. According to the calculations performed by Fulle (1992) the P/SW1 apparently provides of the mass required to balance the losses of the interplanetary dust cloud. Furthermore direct radio observations have provided evidence of a CO mass loss rate close to 2000  kg  s^-1 (Senay & Jewitt 1994), so that the inverse tail model output becomes a realistic lower limit of actual dust mass loss rate. Since the meteoroid supply from trans-Jupiter sources is ruled by Jupiter perturbations on the dust orbits, an original result of this paper will be the estimate of the percentage of meteoroids which enter the Jupiter orbit. Taking into account the results on the emission anisotropy and velocity provided by inverse tail model, it is possible to follow the orbital evolution of dust grains leaving the parent comet with a relative velocity different from zero. The trajectories of the particles are then integrated in the context of a nine-body problem (Sun, seven major planets and the dust particle) with the solar radiation and wind forces accounted for.

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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