An Oort Cloud origin of the Halley-type comets

The origin of the Halley-type comets (HTCs) is one of the last mysteries of the dynamical evolution of the solar system. Prior investigation into their origin has focused on two source regions: the Oort Cloud and the scattered disc. From the former it has been difficult to reproduce the non-isotropic, prograde skew in the inclination distribution of the observed HTCs without invoking a multi-component Oort Cloud model and specific fading of the comets. The scattered disc origin fares better, but needs an order of magnitude more mass than is consistent with theory and observations. Here we revisit the Oort Cloud origin and include cometary fading. Our observational sample stems from the JPL catalogue. We only keep comets discovered and observed after 1950, but place no a priori restriction on the maximum perihelion distance of observational completeness. We then numerically evolve half a million comets from the Oort Cloud through the realm of the giant planets and keep track of their number of perihelion passages with perihelion distance q 2.3 km and q < 1.8 AU is on the order of 100