THE ORIGIN OF SHORT-PERIOD COMETS

Recent work has shown that if short-period comets predominantly occur as a result of planetary "captures" of long-period comets, the relevant source flux of nearly parabolic orbits must involve comets with perihelia in the range 5-30 AU, significantly beyond the region in which the flux is observationally constrained. The numbers and orbital parameters of short-period comets therefore in principle provide strong constraints on those theories of cometary origin which predict the existence of a massive inner core to the Oort cloud. Short-period comets now play a role in relation to the inner core as important as that formerly played by the observed near-parabolic flux in relation to the Oort cloud beyond r {reversed tilde equals} 2 × 104 AU. © 1990.