ORIGIN OF SHORT-PERIOD COMETS

Reasons for interest in the origin of short-period comets and the difficulties of computing their long-term dynamical evolution are reviewed. The relative advantages of a source region in an extended 'inner core' of the Oort cloud or a compact 'comet belt' just beyond the planetary system are finely balanced, and it is premature to consider the problem solved. A complication is that some cornets belonging to the Jupiter family may be part of a time-dependent system, possibly the remains of a giant comet such as Chiron which could have been part of the system approximate to 10(4) yr ago. The origin of short-period comets plays a pivotal role in many areas of solar system science: planet formation, the source of water (possibly life) on the terrestrial planets, the cratering record on the terrestrial planets and satellites of the outer planets, and the environmental impact posed by massive bodies and their decay products in the Earth's near-space environment.