Neptune

Neptune is the eighth planet from the Sun, and the farthest planet from the Sun in the Solar System. Neptune was discovered on September 23, 1846 by three astronomers: John Couch Adams, Urbain Le Verrier, and Johann Galle. Neptune has fourteen known satellites. Neptune has the fastest winds in the Solar System, reaching more than 1200 miles per hour toward the equator.

Formation
Neptune, like all of the gas giants, were formed by a nebula cloud which also formed the rest of the planets. Yet, because it was formed such a distance from the Sun, it did not become a rocky planet and stayed a gas planet.

Composition
The composition of Neptune is similar to that of Uranus in size and interior. In fact, to emphasize the distinctions between the two from the other gas giants Jupiter and Saturn, Neptune and Uranus have been categorized with the term of "ice giants" due to there being an exceptional amount of freezing compounds of carbon and ammonia in the atmosphere, which can lead to frozen water in the atmosphere and the surface.

Internal Structure
The internal structure of Neptune is similar to that of the neighboring planet of Uranus. The first layer is the mantle, which makes up the mass of Neptune. The mantle consists of a water-ammonia compound and methane. In fact, the water-ammonia compound makes up so much of the mantle, scientists refer to it as a water-ammonia ocean. The core of Neptune is mostly made up rock silicates such as iron and nickel.

Rings
Neptune has its own collection of rings called the Rings of Neptune. These rings were discovered in the La Silla Observatory in Chile by Reinhold Häfner, Patrice Bouchet, and Jean Manfriod. These rings very lowly dense. Even at their densest, they are only as dense as the lesser dense parts of Saturn's rings. The innermost moons in the rings include Despina, Naiad, Thalassa, and Galatea. The outermost moons in the rings include Larissa and Prometheus.

Orbit and Rotation
Neptune makes only one orbit around the Sun in about 168 Earth years. This is because Neptune is more than two billion miles from the Sun.

Because of its gaseous nature, Neptune's equatorial rotation is equal to 18 Earth hours. Yet since the wind speeds towards the poles are faster, the polar rotation is equal to 12 Earth hours.

Atmosphere
Most of the atmosphere of Neptune is made up of hydrogen, making up more than eighty percent of the atmosphere. The rest is made of helium, methane, hydrogen deuteride, and ethane.

Great Dark Spot
The Great Dark Spot, is a dark spot on the surface of the planet, Neptune. This one has many similar characteristics to the more famous, and commonly mistaken for, Great Red Spot. One example of a similarity is the category of the storm, for they are both anticyclonic storms, or storms that rotate different directions than that of regular storms, which are referred to as cyclonic. The first spot was observed by the Voyager 2 probe in 1989. The interior of these spots are cloud-free compared to that of Jupiter's Great Red Spot, which densely packed with dust-filled clouds. Winds in this storm are the fastest in the Solar System, being 1500 miles per hour.

Dimensions
The dimensions of the GDS were estimated by scientists in 1995. The dimensions measured were 15,900 x 9870 x 8350 x 4100 miles.

Disappearance
In November of 1994, the Hubble Space Telescope failed to photograph the GDS, leading scientists to believe that it has disappeared. Many theories surround this disappearance - one such theory claiming that due to the high wind speeds of the cyclones, as well as their close proximity to one another, the storms all pushed themselves into different directions. Another one is that they were covered up by an abundance of dust kicked into the atmosphere.

The Northern Great Dark Spot
After the disappearance of the main Great Dark Spot, a new, similar spot formed the northern hemisphere of Neptune. It was given the name of the Northern Great Dark Spot, or NGDS. It is the last one remaining, and has lasted several years.