The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It was formed 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is an ordinary main sequence star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere. Montage of the largest bodies in the Solar System. The asteroid belt and Kuiper belt.