Shortly after its discovery, Neptune was temporarily called "the planet exterior to Uranus" or "Le Verrier's planet". The first suggestion for a name came from Galle. He proposed the name "Janus". In England, Challis suggested the name "Oceanus". In France, Arago suggested that the new planet be called "Leverrier", a suggestion which was met with a lot of opposition outside France. French almanacs quickly reintroduced the name "Herschel" for "Uranus" and "Leverrier" for the new planet.
Meanwhile, Adams suggested changing the name "Georgian" to "Uranus", while Leverrier (through the Board of Longitude) suggested "Neptune" for the new planet. Struve gave support of that name on 29 December 1846, to the Saint Petersburg Academy of Sciences. Soon "Neptune" was internationally agreed among many people. It was the official name for the new planet. In Roman mythology, Neptune was the god of the sea, identified with the Greek god, Poseidon.
At 102.413kg, Neptune's mass puts the planet between Earth and the largest gas giants. Neptune has seventeen Earth masses but just 1/18th the mass of Jupiter. Neptune and Uranus are often considered to be part of a sub-class of a gas giant known as ""ice giants"." It is given their smaller size and big differences in composition compared to Jupiter and Saturn. In the search for extrasolar planets, Neptune has been used as a reference to determine the size and structure of the discovered planet. Some discovered planets that have similar masses like Neptune are often called "Neptunes."
The atmosphere of Neptune is made up mostly of hydrogen, with a smaller amount of helium. A tiny amount of methane was also detected in the atmosphere. The methane gives Neptune its blue color.
Because of Neptune's far distance from the Sun, it gets very little heat. The average temperature on Neptune is about -201°C (−331 °F; 72 K). Therefore, Neptune is the coldest planet in the Solar System. But in the depths of planet the temperature rises slowly. The source of this heating is unknown. Neptune is the farthest planet from the Sun, yet its internal energy is strong enough to create the fastest winds seen in the Solar System. Several possible explanations have been suggested. Firstly, radiogenic heating from the planet's core. Among the explanations is the continued radiation into space of leftover heat made by infalling matter during the planet's birth. The last explanation is gravity waves breaking above the tropopause.
The structure of the inside of Neptune is thought to be very similar to the structure of the inside of Uranus. There is likely to be a core, thought to be about 15 Earth masses. It is made up of molten rock and metal surrounded by rock, water, ammonia, and methane. This mixture is referred to as icy. It is called a water-ammonia ocean. More mixtures of methane, ammonia, and water are found in the lower areas of the atmosphere.
At a depth of 7, 000 km of Neptune, the conditions may be such that methane decomposes into the diamond crystals. These diamond crystals resemble hailstones.
The pressure at the center of Neptune is millions of times more than that on the surface of Earth.
One difference between Neptune and Uranus is the level of meteorological activity that has been observed. When the Voyager spacecraft flew by Uranus in 1986, the winds on that planet were observed to be mild. When Voyager flew by Neptune in 1989, powerful weather events were observed. The weather of Neptune has extremely active storm systems. It's atmosphere has the highest wind speeds in the Solar System, thought to be powered by internal heat flow. Regular winds in the equatorial region have speeds of around 1,200 km/h (750 mph). Winds in storm systems can reach up to 2,100 km/h, near-supersonic speeds.
In 1989, the Great Dark Spot, an anticyclonic storm system, was discovered by NASA's "Voyager 2" spacecraft. The storm resembled the Great Red Spot of Jupiter. However, on 2 November 1994, the Hubble Space Telescope did not see the Great Dark Spot on the planet. Instead, a new storm similar to the Great Dark Spot was found in the planet's northern hemisphere. The reason why the Great Dark Spot has disappeared is unknown. The Scooter is another storm, a white cloud group farther south than the Great Dark Spot. Its nickname was given when first noticed in the months leading up to the "Voyager" encounter in 1989. It moved faster than the Great Dark Spot. Later images showed clouds that moved even faster than Scooter. The Wizard's Eye/"Dark Spot 2" is another southern cyclonic storm, the second strongest storm seen during the 1989 encounter. It originally was completely dark, but as "Voyager" came closer to the planet, a bright core developed.
Neptune also has similarities with Uranus in its magnetosphere. The magnetic field strongly tilted comparative to its rotational axis at 47° and offset at least 0.55 radii (about 13,500 kilometres) from the planet's physical center. The scientists think the extreme course may be characteristic of flows in the interior of the planet.
Tiny blue-colored rings have been discovered around the blue planet. They are not as well known as the rings of Saturn. When these rings were discovered by a team led by Edward Guinan, originally, they thought that the rings might not be complete. However, this was proven wrong by "Voyager 2". Neptune's planetary rings have a weird "clumpy" arrangement. The scientists think that it may be because of the gravitational contact with small moons that orbit near them.
Proof that the rings are incomplete first began in the mid-1980s, when stellar occultation were found to rarely show an extra "blink" just before or after the planet occulted the star. Pictures from "Voyager 2" in 1989 solved the problem when the ring system was found to have several faint rings. The farthest ring, Adams, has three famous arcs now named "Liberté", "Egalité", and "Fraternité" (Liberty, Equality, and Fraternity).
The existence of arcs is tough to understand because the laws of motion would predict that arcs spread out into a single ring in a very short time. The gravitational effects of Galatea, a moon just inward from the ring, are now thought to have created the arcs.
New Earth-based observations published in 2005 appeared to show that Neptune's rings are a lot more unstable than thought before. To be exact, it looks like that the "Liberté" ring may disappear in less than 100 years. The new observations seem to puzzle our understanding of Neptune's rings into a lot of confusion.
Neptune has a total of 14 known moons. As Neptune was the Roman god of the sea, the planet's moons were named after lesser sea gods or goddesses.
The largest moon, and the only one big enough to have the shape of a sphere is Triton. Triton was discovered on October 10, 1846 by British astronomer William Lassell. Unlike all other large planetary moons, Triton moves in the other direction than the other moons. This shows the moon was probably captured and maybe was once a Kuiper belt object. It is close enough to Neptune to be locked into a synchronous orbit. It is also slowly moving into Neptune and will one day be torn apart when it passes the Roche limit. Triton is the coldest object that has been measured in the Solar System, with temperatures of −235°C (38 K, −392 °F).
Neptune's second known moon (by order of distance), the odd moon Nereid, has one of the most unusual orbits of any satellite in the Solar System.