From Contraction to Condensation

In 1755, the great German philosopher Immanuel Kant (1724–1804) theorized that the solar system had begun as a nebula—a cloud of dust and gas—that slowly rotated, gradually contracting until it became flattened into a spinning disk that variously coalesced into the sun and planets.
Later, in 1796, the French astronomer and mathematician Pierre-Simon Laplace (1749–1827) suggested a similar hypothesis, though he thought the planets formed before the sun.