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Neptune (planet)

Neptune is the eighth planet from the sun and the farthest known planet in the solar system. It is the fourth-largest planet in the solar system by diameter and the third-most massive planet. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. It has no well-defined solid surface and is composed primarily of gases and liquids. The planet orbits the sun once every 164.8 years at an average distance of 30.1 astronomical units.

Neptune was predicted mathematically rather than by empirical observation due to unexpected changes in the orbit of Uranus. It was subsequently observed with a telescope in 1846, and its largest moon, Triton, was discovered shortly thereafter. Voyager 2 remains the only spacecraft to have visited Neptune, but recent advancements in telescopes have allowed for additional detailed observations from afar.

Photograph taken by NASA's Voyager 2 in 1989. source: wikipedia

source: wikipedia

Order from the sun



Fourth-largest planet in the solar system


1.02413×1026 Kg


Densest giant planet 1.638 g/cm3


Composed primarily of gases and liquids



Orbital period

Once every 164.8 years

Average distance

30.1 astronomical units (4.5 billion km; 2.8 billion mi)

Discovery method

Predicted mathematically due to unexpected changes in the orbit of Uranus

First observation


Largest moon


Visited by spacecraft

Voyager 2