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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.
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