Solar system formation. Artwork showing the formation of the solar system about 4. 5 billion years ago. The Sun and planets are thought to have formed from a nebula (a cloud of gas and dust, left) that collapsed, possibly due to the shock wave from a nearby supernova. The collapse compressed some of the nebula to form a central protostar. Because of its initial rotation, the rest of the material ended up in orbit, forming a rotating accretion disc (centre). As this disc cooled, it condensed into solid particles of metal, rock and ice. Collisions and the effect of gravity caused the particles to stick together or accrete (right), eventually forming the planets.