The Solar System’s Roots and Expansions

The Nebular Hypothesis

Developed by Emanuel Swedenborg in 1734, expanded upon by Immanuel Kant in 1755, and related to the ideas of Pierre-Simon Laplace in 1796, the Nebular Hypothesis is a widely accepted theory that proposes an idea for how the Solar System came to be.

It states that around 4.6 billion years ago, a collapse in a giant cloud of molecular gas (solar nebula) formed the core of what would eventually grow into the Sun. Then, it was a small, rapidly spinning protostar. This protostar spun out the remaining surrounding molecular cloud into a protoplanetary (accretion-like) disk. Eventually, approximately 100 million years later, this disk formed the first planets, moons, and asteroids, and more notably, the gas giants.

Originally in 1734, Swedenborg proposed that planets, among the other early celestial bodies, were formed from a nebular crust surrounding the Sun. Later in 1755, Kant expanded on this idea. He also pointed out that it wouldn’t be a crust, but a disk, as the “crust“ surrounding the Sun was a nebula that would eventually flatten with time and the formation of celestial bodies. Following these advances, Pierre-Simon Laplace proposed a model in 1796 that closely resembled Swedenborg’s and Kant’s. However, in Laplace’s model, he stated that a protosolar cloud condensed into planets, forming the celestial bodies before the Sun.

After all of these proposals, the Nebular Hypothesis was abandoned sometime in the early 20th century primarily due to difficulty in the explaining the angular momentum distribution between the Sun and the planets. The model does not address this despite 99% of planets in the Solar System having some form of angular momentum. However, this wasn’t the end of the theory, as it eventually gave way to other theories, evolving into what would become known as the Solar Nebular Disk Model (SNDM).