<P> Neptune is the 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 . Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 AU ( 4.5 billion 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 . </P>
what type of planet is neptune known as
giant