Flexi Says: Our solar system began about 5 billion years ago. The Sun, planets, and other solar system objects all formed at about the same time. The leading hypothesis for how they formed is called the nebular hypothesis. The Solar Nebula The Sun and planets formed from a giant cloud of gas and dust. This was the solar nebula. The cloud contracted and began to spin. As it contracted, its temperature and pressure increased. The cloud spun faster and formed into a disk. Scientists think the solar system at that time looked like these disk-shaped objects in the Orion Nebula. New stars are forming in the Orion Nebula today.