奥尔特云
Some of the objects scattered onto very distant orbits during the giant planet migration are captured in the Oort cloud. The outer Oort cloud, semi-major axes greater than 20,000 AU, forms quickly as the galactic tide raises the perihelion of object beyond the orbits of the giant planets. The inner Oort cloud forms more slowly, from the outside in, due to the weaker effect of the galactic tide on objects with smaller semi-major axes. Most objects captured in the outer Oort cloud are scattered outward by Saturn, without encountering Jupiter, with some being scattered outward by Uranus and Neptune. Those captured in the inner Oort cloud are primarily scattered outward by Neptune. Roughly 6.5% of the planetesimals beyond Neptune's initial orbit, approximately 1.3 Earth masses, are captured in the Oort cloud with roughly 60% in the inner cloud.