Sol, the primary of the Sol System.

"Outside intelligences, exploring the Solar System with true impartiality, would be quite likely to enter the Sun in their records thus: Star X, spectral class G0, 4 planets plus debris"
―Isaac Asimov

The Sol System, usually called Solar System by its inhabitants, is a single-star system in the Milky Way Galaxy. It is believed to have been formed about 4.6 billion years ago. The primary, Sol, is a yellow class G star orbited by eight planets. The four inner planets – Mercury, Venus, Earth and Mars – are all terrestrial, whereas the outer ones – Jupiter, Saturn, Uranus and Neptune – are gas giants. Between the orbits of Mars and Jupiter lies a large asteroid belt, believed to be the materials of a would-be planet that never formed due to the strong gravitational effects caused by its proximity to Jupiter, which is by far the largest planet of the system. Beyond Neptune there is a vast collection of icy objects known as the Kuiper Belt, which includes three dwarf planets. An additional dwarf planet, Eris, is found further than the Kuiper Belt. Notable moons include Luna, which orbits Earth; the four Galilean moons of JupiterCallisto, Ganymede, Europa and Io; and Titan and Enceladus, which orbit Saturn. Liquid water is extensively present on the surface of Earth and believed to be present under the ice coating of Europa and/or Enceladus, while lakes of liquid methane are present on Titan. In addition, both Venus and Mars are believed to have possessed large oceans in the past. The Sol System is perhaps most notable for being the origin of the Human species and all known organic life as far as our scientific knowledge goes. In science fiction it has also given rise to numerous other intelligent races.


Dwarf planetsEdit

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