Planetary formation. Artwork of a protoplanet forming along with its satellites. It is thought that the planets formed from a rotating disc of gas and dust that surrounded the newly-formed Sun around 4. 6 billion years ago. In an analogous process the condensing planets also formed discs around themselves. Satellites and rings formed from these planetary discs, usually only around the massive gas giants. This gas giant has five large satellites (small yellow spheres) forming around it. This is a similar set- up to the planetary system of Uranus.