Collision hypothesis and accretion hypothesis are described below in short. 1. Collision Hypothesis: It was given by Sir James and Harold Jeffrey. According to this theory, a large nebula ’wandering in the space came very close to smaller nebula (Sun) and its huge upsurge of matter on the surface of smaller nebula. The matter was detected from the smaller nebula and on cooling condensed into planets. 2. Accretion Hypothesis: It was given by? Schmidt and Carl Weizascar. According to them, solar system started out as a cloud of gas and dust drifting in a space called nebula. This gaseous cloud exploded violently to form supernova. The exploitation left the vast spinning cloud and gases and thus to collapse under its own gravity and develop as denser core. The denser core became larger and hotter and began to burge. Later it developed into protostar which finally evolved as ‘infant Sun. Away from its central surface, particles of dust began to clump together and converted into first smaller fragments of rocks and then becoming larger bodies which were called planetesimals which collided with one another to form rocky inner planets like Mercury, Venus, Earth and Mars and the remaining were outer planets.