Planet Nine and inclination, of objects scattered outward by Jupiter and Saturn, leaving some of them in high inclination (inc > 50°), low eccentricity orbits which have not been observed. The gravitational influence of Planet Nine would explain five peculiarities of the Solar System: While other mechanisms have been offered for many of these peculiarities, the gravitational influence of Planet Nine is the only one that explains all five. The gravity of Planet Nine also excites the inclinations of scattered disc objects, which in numerical simulations leaves the short-period comets with a broader inclination distribution than is observed. The clustering of the
Solar System icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four giant planets. Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune. Most of the planets in the Solar System have secondary systems of their own, being orbited by planetary objects called natural satellites, or moons (two of which, Titan and Ganymede, are larger than the planet Mercury), and, in