Solar system planets. Computer artwork of the planets of the Solar System on a huge explosion. Clockwise from lower left, the planets are: Saturn, Mars, Pluto, Jupiter, Mercury, Uranus, Neptune, Venus and the Earth with the Moon to its right. This could represent the Big Bang as the source of all the planets. The Big Bang is one theory to explain the formation of the Universe. It is based on the observation that everything in the visible universe is expanding from one point. It is thought that all matter was formed at this instant. The heavy materials which make up planets are thought to have been formed in stars.