Astronomers believe that the solar system began forming from the great explosion of the big bang, approximately 3.7 billion years ago. The big bang created a gigantic cloud of dust and gas called the solar nebula. This cloud contained several times the mass of the sun that condensed and collapsed into a dense, flat, spinning disk with an extremely hot center. It is thought that the hot central part of the disk gradually became the sun, while the planets and all other objects in the solar system formed from the remaining material.
