JUMPING NEPTUNE CAN EXPLAIN THE KUIPER BELT KERNEL

The Kuiper Belt is a population of icy bodies beyond the orbit of Neptune. A particularly puzzling and up-to-now unexplained feature of the Kuiper Belt is the so-called kernel, a concentration of orbits with semimajor axes a similar or equal to 44 AU, eccentricities e similar to 0.05, and inclinations i < 5 degrees. Here we show that the Kuiper Belt kernel can be explained if Neptune's otherwise smooth migration was interrupted by a discontinuous change of Neptune's semimajor axis when Neptune reached similar or equal to 28 AU. Before the discontinuity happened, planetesimals located at similar to 40 AU were swept into Neptune's 2:1 resonance, and were carried with the migrating resonance outwards. The 2:1 resonance was at similar or equal to 44 AU when Neptune reached similar or equal to 28 AU. If Neptune's semimajor axis changed by fraction of AU at this point, perhaps because Neptune was scattered off of another planet, the 2:1 population would have been released at similar or equal to 44 AU, and would remain there to this day. We show that the orbital distribution of bodies produced in this model provides a good match to the orbital properties of the kernel. If Neptune migration was conveniently slow after the jump, the sweeping 2:1 resonance would deplete the population of bodies at similar or equal to 45-47 AU, thus contributing to the paucity of the low-inclination orbits in this region. Special provisions, probably related to inefficiencies in the accretional growth of sizable objects, are still needed to explain why only a few low-inclination bodies have been so far detected beyond similar or equal to 47 AU.