Neptune, named after the Roman god of the sea, was discovered on September 23, 1846, (the first planet found using mathematics rather than empirical observation). It's the eighth planet from the Sun orbiting at an average distance of 4,503,443,661 km or 30.1 AU, the fourth largest with a diameter of 49,528 km and the third most massive. It is often referred to as a gas giant, but as with Uranus ice giant would probably be more fitting.

Voyager 2 visited the ice giant in 1989 so far the only Earth spacecraft to do so. Its flyby added much to our knowledge base. (A giant storm system similar to the "Great Red Spot" was observed in the southern hemisphere only to later disappear others appearing elsewhere.)

The planet's mantle composed of water, ammonia and methane ices surrounds a small rocky silicate, iron and nickel core. The atmosphere is thin (as compared to the true gas giants Jupiter and Saturn) mainly hydrogen (85%), helium (13%) and methane (2%), and with winds approaching 2,100 km per hour very turbulent. The mean cloud temperature is a frosty -190 degrees Celsius, its core a toasty 5,000 degrees Celsius.

Neptune has a faint ring system [1] composed of six bands of varying thickness, Galle, Le Verrier, Lassell, Arago, unnamed (co-orbits with the moon Galatea), and the furthest out Adams which orbits at a distance of 62,930 km from the planet's center.

To date Neptune has 14 known moons: Naiad, Thalassa, Despina, Galatea, Larissa, S/2004 N 1 (provisional), Proteus, Triton, Nereid, Psamathe, Halimede, Sao, Laomedeia and Neso.

[1] A planetary ring is a flat disk shaped band composed of rock or ice dust, larger rocks, boulders and ice chunks which circle in a planet's equatorial plane.

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