The following
outline is provided as an overview of and topical guide to Neptune:
Neptune – eighth and farthest known
planet from the
Sun in the
Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest
giant planet. Neptune is 17 times the mass of
Earth and is slightly more massive than its near-twin
Uranus, which is 15 times the mass of Earth and slightly larger than Neptune.[a] Neptune orbits the Sun once every 164.8
years at an average distance of 30.1
astronomical units (4.50×109 km). It is named after the
Roman god of the sea and has the
astronomical symbol ♆, a stylised version of the god Neptune's
trident.