A keplerian method to estimate perturbations in the restricted three-body problem

We develop a new and fast method to estimate perturbations by a planet on cometary orbits. This method allows us to identify accurately the cases of large perturbations in a set of fictitious orbits. Hence, it can be used in constructing perturbation samples for Monte Carlo simulations in order to maximize the amount of information. Furthermore, the estimated perturbations are found to yield a good approximation to the real perturbation sample. This is shown by a comparison of the perturbations obtained by the new estimator with the results of numerical integration of regularized equations of motion for the same orbits in the same dynamical model: the three-dimensional elliptic restricted three-body problem (Sun-Jupiter-comet).     

Cometary dynamics

Since comets appear to be observable only at the expense of rapid aging in the vicinity of the Sun, chaotic routes are considered necessary in order to bring them from their remote places of origin and storage. Recent work on short-period cometary orbits has verified this expectation in general terms but has also shown many examples of temporary resonance trappings and other quasiregular phenomena. For long-period comet dynamics recent developments point to the importance of long-term effects associated with the Galactic tidal field acting in conjunction with the randomizing effect of stellar encounters. This paper presents a comprehensive review of all these aspects of cometary dynamics.     

An Extended CO Source around Comet 29P/Schwassmann-Wachmann 1

Comet 29P/Schwassmann-Wachmann 1 has been studied during seven days in August 1998 with the SEST submillimeter telescope at ESO, La Silla, Chile. The CO (J=2−1) emission at 230 GHz was mapped by directing the telescope beam at the nucleus and six off-nucleus positions. The CO line profiles exhibit the blue- and redshifted components previously observed by various observers. The strength of the observed lines does not decrease with projected distance to the nucleus as expected if CO molecules were coming from the nucleus only. Instead, the line area is nearly constant throughout the map. This can be explained if CO molecules are being released from both the sunlit side of the nucleus and CO-bearing particles distributed in a shell-like cloud. The extended source must consist of icy grains globally moving toward the Sun at ∼50 m s⁻¹ released ∼30 days before the observations were made. The nuclear and extended sources produce (7±1)×10²⁷ and 2.4×10²⁸ molecules s⁻¹, respectively. Our 1996 observations of the comet (Festou, M., M. Gunnarsson, A. Winnberg, H. Rickman, and G. Tancredi 2001. Icarus150, 140-150) were reexamined using this new two-source model. In this case, the nuclear and extended CO sources produced 10±1×10²⁷ and 2.9×10²⁸ CO molecules s⁻¹, respectively. It is not necessary to postulate night side outgassing, but a large quantity of solid grains has to be expelled into the coma.     

Structure and evolution of the Jupiter family

Both physical and dynamical issues are important in order to judge the origin and evolution of the Jupiter family of short-period comets. The steady-state condition for maintaining this structure at its present size by captures from the classical Oort cloud is reviewed on the basis of recent results concerning the absolute number of Jupiter family comets as a function of perihelion distance as well as the coupled physical and dynamical evolutions that evidently occur. Like in most earlier investigations, a clear shortage is found in the classical Oort cloud source. The shortage seems, however, less extreme than sometimes assumed. Monte Carlo simulations are envisaged as a way to shed further light on the fate of Jupiter family comets.