In 1796, Pierre-Simon de Laplace, a French astronomers and mathematician, refined Kant's theory, He suggested that Earth was first a gas and then liquid. Over time, according to Laplace, Earth cooled enough to have a solid crust. Laplace's theory became known as the Nebular Hypothesis.

Essentially, the nebula hypothesis states that at some point in the very distant past, a slowly spinning cloud of interstellar gas began to cool, causing it to shrink into a compact sphere; the sphere then began to spin faster in accordance with the law of conservation of angular momentum, a basic tenet of physics stating that a rotating object gets smaller, it spins faster. A familiar example is a spinning ice skater. When both arms are pulled in close to the body, the skater spin faster. The same principle applies to a spinning cloud of gas.

As the great sphere of interstellar gas rotated faster, centrifugal forces came into play, flinging some of the matter within the cloud away from its center. The various bits of far-flung matter settled into rings tracing paths around the gaseous sphere. The rings of matter cooled and condensed into nine planets that continued to rotate around the sphere, which condensed to form a Sun.

In its earliest form, the nebular hypothesis had some serious flaws. About 100 years after Laplace detailed his ideas, Scottish physicist James Clerk Maxwell and Sir James Jeans, an English physicist, noted that it would have required an unreasonable amount of gravitational pull to condense the proposed rings of matter into planets.

Forest Ray Moulton, an astronomer at the University of Chicago, pointed out an other problem with the theory. According to the law of conservation of angular momentum, the most massive part of any spinning system should be rotating at the greatest speed. But in fact, the planets in solar system rotate around the Sun at the rate faster than the Sun's own rotation. Thus, it is not possible that they were once part of the same spinning cloud.  


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