This hypothesis was put forward by Kant, the German philosopher in 1755; and Laplace, the French Mathematician in 1796. It says that the solar system – the earth and the other eight planets and the sun itself has originated from a nebula. The Nebular hypothesis may be summarized as follows.
- Originally there was a large, hot gaseous nebula rotated slowly.
- Gradually it cooled and contracted. Due to contraction the speed of rotation about its axis increased and the centrifugal force in the equatorial zone also increased. The nebula, therefore, bulged out in the equatorial zone and ultimately a gaseous ring was separated out.
- Later on the ring cooled and condensed to form a planet.
- The process of ring formation was repeated and all the nine planets of the solar system came into existence. Planetoids were formed when one such ring broke into many small fragments.
- The central mass of the nebula contracted and became the sun.
According to this hypothesis, the sun should have the greatest angular momentum because it has the largest mass and is situated at the center of the solar system. But actually the sun has only 2% of the angular momentum of the solar system. This is the serious objection to this hypothesis. Further, it is not known how the hot gaseous material condensed into rings.