The decay of short period comets
This thesis considers both the mass of dust released by short period comets and the size distribution of a decaying cometary population. The secular variation in the H 10 absolute magnitude of comets 2P /Encke, 4P /Paye, 6P /d'Arrest, 7P /Pons-Winnecke and lOP/Tempel 2 is investigated and it is concluded that there is more information in the H 10 data than can be found from a linear regression analysis. A computer program is presented that takes the absolute magnitude of a comet, H 10, the orbital eccentricity and the perihelion distance, and calculates the mass of dust released by the comet per apparition. This model is applied to the H1O data set for the above comets, and it is concluded that 4P /Paye has been a prolific contributor of dust to the inner Solar System, releasing an average of (21.6 ± D.5) x 1011 g per apparition during the last 19 recorded apparitions. This is mainly attributed to an unusual period of activity pre-1910. A simple model of cometary decay, whereby individual comets lose a constant depth from the cometary nucleus at each apparition is presented. This is used to model the decay of a model population of short period comets. The population is examined at regular time intervals and the mass distribution index is calculated. This index indicates how mass is distributed within the cometary population, and is found to decrease, non-linearly, as comets in the population decay. The total mass of dust released by a model population of comets, each having only one perihelion passage, is also calculated. The list of cometary orbits for this population is kept fixed and the cometary H1O values are randomly mixed up and reassigned back to the list of orbits. In this way new populations of short period comets are created. It is concluded that the current population of short period comets releases an unusually small total mass of dust, and that this is due to the average value of H10 decreasing as a function of perihelion distance.