Some statistical aspects of cometary orbits and their discoveries

Abstract

The study of the cometary orbital elements available in the tenth edition of the 'Catalogue of Cometary Orbits' (Marsden and Williams, 1995) which hereafter will be written as the 'Catalogue 1995' and the perpetual discoveries of comets reveal various interesting features. The 'Catalogue 1995' contains 1472 orbital elements of 878 individual comets which were possible to observe for displaying 1444 apparitions during the period from 239 B.C. to 1994 A.D. Among these comets, 184 are designated as the Short Period (SP) comets, for having periods less than 200 years. The remaining 694 comets, are termed as the Long Period (LP) comets, since their periods are longer than 200 years. All the orbital elements have been studied thoroughly and found how the orbital inclinations, perihelion distances and aphelion distances are distributed. The analysis of the proximity of aphelia distances of SP comet orbits from their respective nearby planetary orbits reveals that the orbits of major planets are closely visited by most of the SP comet aphelia. The set of comets whose aphelia closely visit a particular planetary orbit, are said to constitute a family of comets of the said planet. Classifying these comets, it has been noticed that the Jupiter Family of Comets (JFC) are the largest in number. Also the nodal distances of all the comets have been studied in respect of their distributions. It has been found that 91% of the nodes are within the orbital distance of the planet Neptune at 30 AU away from the Sun. The consequences of the aphelia and nodes of the SP comets being closer to their nearby planetary orbits, have been studied. This study justifies the existence of a number of multiple nuclei comets as well as predicts the possible split of a few more SP cometary nuclei which may finally crash into any one of the perturbing major planetary globes, like the one C/1993 F2 (Shoemaker-Levy 9). Interestingly, it can be inferred from these studies that any group of comets having almost identical orbital elements, may be the outcome of the split suffered by their parent cometary nuclei at a distance far away from the Sun. The discovery of comets was initiated by Gottfried Kirch in 1680 and the recovery of periodic comets was first done by J.G. Palitzsch in 1758. The rate at which the comets are discovered and also recovered, have been shown. Key Words : cometary orbits, orbital elements, nodal distributions, split comets, cometary discovery.