Detailed overview of the Nebular Hypothesis of Laplace, including its introduction, assumptions, and theoretical framework. Learn about the formation of planets and the Sun, and evaluate the strengths and limitations of Laplace's hypothesis in explaining planetary formation.

Nebular Hypothesis of Laplace: Introduction

• Laplace (French Mathematician) propounded his theory in 1796.
• The Nebular Hypothesis of Laplace was similar to the Gaseous Hypothesis of Kant and appears as a modified version.

Assumptions

• Laplace assumed that:
  • There was a huge and hot gaseous nebula in space.
  • The nebula was rotating on its axis from the very beginning.
  • The nebula was continuously cooling due to heat loss from its outer surface through radiation.
  • As a result, the nebula was reducing in size due to contraction caused by cooling.

According to Laplace

• Laplace stated that:
  • The nebula was continuously reducing in size due to gradual heat loss through radiation.
  • This reduction in size and volume increased the circular velocity (rotatory motion) of the nebula.
  • With the increase in velocity, the nebula started spinning at a very fast speed.
  • The centrifugal force became so great that it exceeded the centripetal force.
  • The outer surface of the nebula condensed due to excessive cooling, making it unable to rotate with the still cooling and contracting central nucleus.
  • As a result, the outer ring separated from the remaining part of the nebula and started moving around it.
  • Laplace further maintained that:
    • The original ring divided into nine rings.
    • Each ring moved away from the outer ring, forming nine planets.
    • The remaining central nucleus of the nebula became the Sun.

Evaluation

• Laplace did not describe the source of the origin of the nebula.
• He did not explain why only nine rings came out from the irregular ring detached from the nebula.
• If the Sun is the remaining nucleus of the nebula, it should have a small bulge around its middle part, but there is no such bulge in the middle part of the Sun.
• According to the Nebular Hypothesis, all satellites should revolve in the direction of their father planets, but a few satellites of Saturn and Jupiter revolve in the opposite direction.
• The Nebular Hypothesis is unable to explain the peculiar distribution of present-day angular momentum in our solar system.
• Outcome: The merit of the theory lies in its being the most acceptable explanation for the layered structure of the Earth’s interior.