Solar system formation. Artwork of the early solar system being formed. It is thought that the Sun and the planets formed from a cloud of gas and dust around 4. 6 billion years ago. Gravitational condensation of this cloud (or nebula) formed a protostar (lower centre) which has ignited under its own weight. The remaining material forms a rotating disc around this newly-formed Sun. The planets are forming from the disc by accretion, a slow process of gravitational attraction. This formation of a disc occurs throughout the universe as it follows from a universal law requiring the conservation of a rotational property (angular momentum) of the collapsing nebula.