There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud.

alt=Diagram of the Sun and the planets of the Solar System up to Jupiter, including three fictional planets: Vulcan, inside the orbit of Mercury; Counter-Earth, on the opposite side of the Sun from the Earth in the same orbit; and Phaëton, between Mars and Jupiter in the location of the asteroid belt.|thumb|upright=1.35|Schematic diagram of the orbits of the fictional planets Vulcan, Counter-Earth, and Phaëton in relation to the five innermost planets of the Solar System.

The stability of the Solar System is a subject of much inquiry in astronomy.

observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood".