DYNAMICAL EVOLUTION OF COMETARY ASTEROIDS

We present results from long-term numerical integrations of hypothetic al Jupiter-family comets (JFCs) over time-scales in excess of the esti mated cometary active lifetime. During inactive periods these bodies c ould be considered as 'cometary' near-Earth objects (NEOs) or 'cometar y asteroids'. The contribution of cometary asteroids to the NEO popula tion has important implications not only for understanding the origin of inner Solar system bodies but also for a correct assessment of the impact hazard presented to the Earth by small bodies throughout the So lar system. We investigate the transfer probabilities on to 'decoupled ' subJovian orbits by both gravitational and non-gravitational mechani sms, and estimate the overall inactive cometary contribution to the NE O population. Considering gravitational mechanisms alone, more than 90 per cent of decoupled NEOs are likely to have their origin in the mai n asteroid belt. When non-gravitational forces are included, in a simp le model, the rate of production of decoupled NEOs from JFC orbits bec omes comparable to the estimated injection rate of fragments from the main belt. The Jupiter-family (non-decoupled) cometary asteroid popula tion is estimated to be of the order of a few hundred to a few thousan d bodies, depending on the assumed cometary active lifetime and the ad opted source region.