The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into. PastThe Solar System formed at least 4.568 billion years ago from the gravitational collapse of a region within a large. This initial cloud was likely several light-years. The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 ), which comprises 99.86% of all. The inner Solar System is the region comprising the terrestrial planets and the. Composed mainly of and metals, the objects of. Beyond the orbit of Neptune lies the area of the "", with the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets, and an overlapping disc of. Astronomers sometimes divide the Solar System structure into separate regions. The includes Mercury, Venus, Earth, Mars, and the bodies in the. The includes Jupiter, Saturn, Uranus, Neptune, and the bodies in the The outer region of the Solar System is home to the and their large moons. The and many orbit. CometsComets are, typically only a few kilometers across, composed largely of volatile ices. They have highly eccentric.