Final answer:
The Nebular model attributes the formation of two types of planets to nebular collapse, which caused the solar nebula to spin faster and flatten into a disk, leading to differentiated planet formation.
Step-by-step explanation:
The Nebular model explains why there are two kinds of planets based on the concept of nebular collapse. During the formation of the Solar System, a large cloud of gas and dust, known as the solar nebula, began to collapse under its own gravity. This collapse conserved the nebula's angular momentum, causing it to rotate faster and flatten into a disk. Material near the rotational poles fell towards the center, forming the Sun, while the rest of the material in the faster moving equatorial regions of the disk coalesced to form the planets. This rotating disk is responsible for the planets all orbiting the Sun in the same direction and helps define the layout of our solar system today.
Moreover, the process of planet formation involved accretion of planetesimals and was influenced by violent impacts which can explain certain irregularities in the solar system, such as the unique spins of Venus and Uranus. The giant planets were able to attract gas from the solar nebula, leading to their different compositions compared to the terrestrial planets. Thus, the formation of the two types of planets—terrestrial and gas giants—is primarily a result of the nebular collapse and subsequent processes.