Solar system formation. Artwork of rocks found in the protoplanetary disc of the newly-formed Sun in the early solar system. It is thought that the Sun (upper centre) formed from a collapsing nebula around 4.6 billion years ago. The remaining dust and gas formed a rotating disc surrounding the newly-formed Sun. Slow gravitational attraction (accretion) of small particles formed these rocky asteroids (planetesimals). They in turn clumped together to form Earth-like planets or remained scattered like the present-day asteroid belt.