Neptune is the eighth planet from the Sun making it the most distant in the solar system.

It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, and slightly more massive than fellow ice giant Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere.

Neptune is not visible to the unaided eye and is the only planet in the Solar System that was found from mathematical predictions derived from indirect observations rather than being initially observed by direct empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to hypothesise that its orbit was subject to gravitational perturbation by an unknown planet.

Neptune Facts

  • Equatorial Diameter: 49,528 km
  • Polar Diameter: 48,682 km
  • Mass: 1.02 x 10^26 kg (17 Earths)
  • Moons: 14 (Triton)
  • Rings: 5
  • Orbit Distance: 4,498,396,441 km (30.10 AU)
  • Orbit Period: 60,190 days (164.8 years)
  • Surface Temperature: -201°C
  • Discovery Date: September 23rd 1846
  • Discovered By: Urbain Le Verrier & Johann Galle