The planet Neptune was discovered on September 23, 1846 due to mathematical predictions by Urbain Jean Joseph Le Verrier. Neptune was named for the Roman god of the sea. The data was used by Johann Gottfried Galle and Louis d’Arrest to successfully find Neptune. It is the eighth to the farthest planet from the sun (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto). It has thirteen moons, six of which were recently discovered by the satellite Voyager 2. The last five were discovered in 2002 and 2003 using telescopes from the ground. The Great Dark Spot of Neptune changed position from southern Neptune to northern Neptune in 1994.
The mean distance from the sun is 4,504,300,000 kilometers. Neptune and Pluto are the only two planets that cannot be seen without a telescope. The atmospheric composition is 85% hydrogen, 13% helium, 2% methane. The surface of Neptune is composed of hydrogen, helium, water, and silicates. Neptune is covered by layers of blue clouds that are mostly composed of frozen Methane. Winds blow the clouds at speeds of 1,100 kilometers per hour.
The mass of Neptune is 1.024×10^16 kilograms. The equatorial radius is 24,756 kilometers. It takes 165 years to orbit the sun. The day on the planet is about 16 hours. It is one of the Giant or Jovian planets. The Jovian planets (named after Jupiter) in order of size are Jupiter, Saturn, Uranus, and Neptune.
The thirteen satellites of Neptune are named Triton, Thalassa, Proteus, Nereid, Naiad, Larissa, Galatea, Despina, Halimede, Sao, Psamathe, Laomedeia, and Neso. Triton has a diameter of 2,700 kilometers, making it the largest natural satellite of Neptune. It was discovered by the British astronomer William Lassell on October 10, 1846 (less than one month after the discovery of Neptune). Its mass is 2.14×10^22 kilometers. It is 354,800 kilometers from Neptune. Voyager 2 sent back pictures of eruptions of nitrogen gas and dust particles on Triton’s surface. The mean surface temperature is -235 degrees celsius. The escape velocity is 1.45 kilometers per second. Gereid Kuiper found Neptune’s third-largest moon Neried in 1949. It has an equatorial radius of 170 kilometers. Its distance from Neptune is 5,513,400 kilometers. It takes 360 days to orbit Neptune because of its distance from Neptune. One of the six satellites of Neptune discovered by Voyager 2, Proteus, is the second-largest of the satellites of Neptune.
Saturn has the most obvious ring system in the solar system. A ring system for Neptune was not discovered until the 1980s. Voyager 2 discovered a ring system in 1989. The outermost arc is 63,000 kilometers from the planet Neptune and is named Adams. It has three faint arcs named liberty, Equality, and Fraternity. The Leverierr ring is 53,000 kilometers from Neptune and the Galle ring is 42,000 kilometers.