Interplanetary dust dynamics: II. Poynting-Robertson drag and planetary perturbations on cometary dust

Abstract

A statistical analysis of a portion of the calculated orbital evolution of some 200 cometary dust particles as they spiral from just inside the orbit of Jupiter to within 0.3 AU from the Sun reveals an increase in the descent rate as calculated for drag forces alone (i.e., Poynting-Robertson drag and corpuscular drag). This increase appears when planetary perturbations are accounted for in the orbital integrations and are, at least in part, due to planet-induced orbital eccentricities leading to enlarged drag. Trajectories originating from Comet P/Encke are thought to be representative of debris from short-period comets due in part to a redistribution in orbital elements while the dust crossed Jupiter's orbit. Statistical methods indicate that any dependence of the increased descent rate on orbital elements other than semimajor axis and eccentricity were insignificant. There are indications that the planet-induced acceleration of the mean descent rate decreases with decreasing eccentricity. The increase in mean descent rate is only a few percent inside 1 AU; it increases to 6–10% in the asteroid belt and reaches 50% in the 31 resonance with Jupiter. By contrast, the mean rate is slower near the 41 Jovian commensurability than in nearby regions of phase space. An empirical relation is presented for the descent rate of cometary dust particles subjected to planetary perturbations in addition to Poynting-Robertson and corpuscular drags. The analytic expression is suitable to improve estimates of the contribution from short-period comets' to the zodiacal dust, and the resulting particle number density distribution.