Solar system formation. Artwork of rocky asteroids found in the accretion disc of the newly-formed Sun in the early solar system. It is thought that the Sun (centre right) formed from a collapsing nebula around 4. 6 billion years ago. The remaining material formed a rotating disc surrounding the newly-formed Sun. Slow gravitational attraction (accretion) of small particles formed these rocky asteroids (planetesimals). They in turn may clump together to form Earth-like planets or remain scattered like the present-day asteroid belt.