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Easy Explanation of Nebular Hypothesis Theory ! UPSC Geography

The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems).

The theory was developed by Immanuel Kant.

When our solar system was first created all that was thought to have existed was a cold spinning cloud of gas and dust called Solar Nebula. The nebula consisted of basically Hydrogen, Helium and Dust. The Solar nebula resulted from the uneven distribution of gases throughout the universe. As the gravitational pull began to condense the gases towards the centre of the cloud the speed of the rotation of the cloud increased which caused the cloud to flatten and form an accretion disk.

The matter continued to collect as the growing force of the gravity drew it towards the centre. Eventually the gas warmed from the increasing pressure. As the the mass further increased the gravity also increased and as a result the temperature continued to rise.

A ball of hot gas formed at the centre of the accretion disk creating a PROTOSTAR also know as the sun. When enough gas got collected at the centre of the PROTOSTAR the pressure generated enough heat to fuse the atoms forming the star.

Outside the star the matter was forming in clumps of gas, dust and rock which created PROTOPLANETS. These protoplanets continued to grow as they trapped material in their gravitational fields. Because the Protoplanets were formed from the same cloud of gas and dust , they revolve around the Sun in the same direction and in the same plane.

The theory also explains how planets are arranged around the sun. The heat and the solar winds caused by the sun swept the lighter gases far out in the solar system. This is the reason why rock planets ie Mercury, Venus , Earth and Mars are located closer to the sun. The Gas giants ie Jupiter, Saturn, Uranus and Neptune formed in the cooler outer region of the solar system.

The theory answers important questions such as : Q1. Why inner planets are rocky? Ans. Let's look at the three reasons : A. Rocky planets lie near to the sun so it was too warm for the gases to condense

B. The solar wind blew off gases & dust to far space.

C. Due to small size of the planets, the gravitational force generated by them was low and hence could not hold gases.


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