Solar system formation. Artwork showing the primordial cloud of gas from which the solar system originated. The planets in the solar system formed about 4.6 billion years ago following a process of condensation within the primordial nebula. A protostar, the future Sun, is seen in the centre of the nebula; it is characterised by a strong stellar wind which is blowing away gas in a direction perpendicular to the nebula. The planets in the early days underwent a massive bombardment from asteroids and smaller bodies which were populating the interplanetary space. The rate of these collisions has decreased by about 2000 times since then.