Solar system gas giant planets
type: Concept
narrower: Neptune

Neptunian satellites
type: Concept
related: Neptune

Neptune
type: Concept
contributor: AAS Frey.Katie
contributor: AAS Frey.Katie Admin
broader: Solar system gas giant planets
modified: 2020-11-10T19:41:43.352Z
modified: 2020-11-24T17:19:05.278Z
definition: The eighth planet from the Sun and the fourth largest by size in the solar system. The equatorial radius of Neptune is 24,764 km (3.883 Earths), its semi-major axis is 30.11 astronomical units (4.50 x 10^9 km), and its orbital period is 164.8 yr. Neptune has at least 14 moons, the largest ones are Triton, Proteus, and Nereid, whereas its smaller moons are: Naiad, Thalassa, Despina, Galatea, Larissa, Halimede, Sao, Laomedeia, Psamathe, and Neso. Neptune has an incredibly thick atmosphere comprised of 74% hydrogen, 25% helium, and approximately 1% methane. Particles of icy methane in its upper atmosphere give Neptune its deep blue color. Large storms whirl through Neptune's upper atmosphere, and high-speed winds track around the planet at up 600 m/s, fastest recorded in the solar system. One of the largest storms ever seen was recorded in 1989. Called the Great Dark Spot, it lasted about five years. Neptune has a very thin collection of rings. They are likely made up of ice particles mixed with dust grains and possibly coated with a carbon-based substance.
related: Neptunian satellites