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Outermost Planet of the Solar System

Proper NameNeptune
Sidereal Period164.90 years
Mean Distance from the Sun4,504.5 million km
30.11 AU
Sidereal Day18 hours, 12 minutes
Diameter50,538 km
Mean Surface Temperature-193°C
MoonsDespina, Galatea, Halimede, Laomedeia, Larissa, Naiad, Nereid, Neso, Proteus, Psamathe, Sao, Thalassa, Triton; other small moons
NotesThe outermost of the eight major planets of the Solar System, the ice giant Neptune pursues a distant orbit that carries it around the inner edge of the region known as the Kuiper Belt.

Because Pluto pursues an eccentric orbit in comparison with the other worlds of the Solar System, Neptune is periodically the farthest planet from the Sun. This gas giant follows its course on the outer fringes of the Solar System.


The cold, blue world of Neptune, outermost of the gas giants.

Size Comparison of Neptune

With a diameter of 49,500km, Neptune is the smallest of the Jovian planets. In comparison to our own Earth, though, it is gigantic.


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