Nebular hypothesis
Also called: Kant-Laplace hypothesis · Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Class 11, Ch 2 "The Origin and Evolution of the Earth"
Meaning
The nebular hypothesis was an early idea about how the planets formed. It says the planets grew out of a cloud of material around a young sun that was turning slowly. The German philosopher Immanuel Kant proposed it, and the mathematician Laplace revised it in 1796. It matters because a later, improved version of it is still the basis of today's model of how the solar system formed.
Example
In our solar system, all eight planets go round the Sun in the same direction and in almost the same flat plane. This is what you would expect if they all came from one spinning cloud around the young Sun.
Don't confuse with
- Planetesimal hypothesis (Chamberlin and Moulton): this idea said a passing star pulled material out of the Sun. The nebular hypothesis needs no second star.
- Revised nebular hypothesis (1950): this later version, by Otto Schmidt and Carl Weizsacker, added the disc of gas and dust and the growth of planets by accretion.