Early solar system. Artwork of the early solar system at a stage where the planets are still forming. One theory postulates that around 3 to 4.5 billion years ago the planets were much closer together. Also, it suggests that they were not in the orbits they inhabit today. As the early gas giants moved, they collected the debris that was thickly distributed in the younger solar system, with Jupiter stealing material that would have allowed Mars to become larger than it eventually was. Here, rocky debris is colliding with a red Sun in the background.