Formation and evolution of the Solar System | Pre-solar nebula
Pre-solar nebula The nebular hypothesis says that the Solar System formed from the gravitational collapse of a fragment of a giant molecular cloud . The cloud was about 20 parsec (65 light years) across, while the fragments were roughly 1 parsec (three and a quarter light-years ) across. The further collapse of the fragments led to the formation of dense cores 0.01–0.1 pc (2,000–20,000 AU ) in size. One of these collapsing fragments (known as the pre-solar nebula ) formed what became the Solar System. The composition of this region with a mass just over that of the Sun was about the same as that of the Sun today, with hydrogen , along with helium and trace amounts of lithium produced by Big Bang nucleosynthesis , forming about 98% of its mass. The remaining 2% of the mass consisted of heavier elements that were created by nucleosynthesis in earlier gen...