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Previous: The Solar System
It is thought that the Solar System formed according to what is
known as the Nebular Hypothesis. About 4.5 billion years ago
it is believed that the Solar System consisted of a large cloud
of gas and dust, called a nebula. This cloud started
rotating, and the dust particles combined to form planetesimals.
As the cloud rotated faster, it flattened, and the planetesimals
combined to form, first of all, the Sun at the center, and secondly,
the planets in orbit around the Sun. This model explains qualitatively
many features of the Solar System, including the fact that the planets
essentially all revolve around the Sun in the same plane.