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Overview
Neptune is the eighth planet from the sun. It was the first planet to get its existence predicted by mathematical calculations before it was actually seen through a telescope on Sept. 23, 1846. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest that the gravitational pull from another celestial body might be responsible. German astronomer Johann Galle then relied on subsequent calculations to help spot Neptune via telescope. Previously, astronomer Galileo Galilei sketched the planet, but he mistook it for a star due to its slow motion. In accordance with all the other planets seen in the sky, this new world was given a name from Greek and Roman mythology — Neptune, the Roman god of the sea.
Physical Characteristics
Neptune's cloud cover has an especially vivid blue tint that is partly due to an as-yet-unidentified compound and the result of the absorption of red light by methane in the planets mostly hydrogen-helium atmosphere. Photos of Neptune reveal a blue planet, and it is often dubbed an ice giant, since it possesses a thick, slushy fluid mix of water, ammonia and methane ices under its atmosphere and is roughly 17 times Earth's mass and nearly 58 times its volume, according to a NASA fact sheet. Neptune's rocky core alone is thought to be roughly equal to Earth's mass, NASA says.
Despite its great distance from the sun, which means it gets little sunlight to help warm and drive its atmosphere, Neptune's winds can reach up to 1,500 mph (2,400 kph), the fastest detected yet in the solar system. These winds were linked with a large dark storm that Voyager 2 tracked in Neptune's southern hemisphere in 1989. This oval-shaped, counterclockwise-spinning "Great Dark Spot" was large enough to contain the entire Earth, and moved westward at nearly 750 mph (1,200 kph). This storm seemed to have vanished when the Hubble Space Telescope later searched for it. Hubble has also revealed the appearance and then fading of two other Great Dark Spots over the past decade.
Neptune's magnetic poles are tipped over by roughly 47 degrees compared with the poles along which it spins. As such, the planet's magnetic field, which is about 27 times more powerful than Earth's, undergoes wild swings during each rotation.
Despite its great distance from the sun, which means it gets little sunlight to help warm and drive its atmosphere, Neptune's winds can reach up to 1,500 mph (2,400 kph), the fastest detected yet in the solar system. These winds were linked with a large dark storm that Voyager 2 tracked in Neptune's southern hemisphere in 1989. This oval-shaped, counterclockwise-spinning "Great Dark Spot" was large enough to contain the entire Earth, and moved westward at nearly 750 mph (1,200 kph). This storm seemed to have vanished when the Hubble Space Telescope later searched for it. Hubble has also revealed the appearance and then fading of two other Great Dark Spots over the past decade.
Neptune's magnetic poles are tipped over by roughly 47 degrees compared with the poles along which it spins. As such, the planet's magnetic field, which is about 27 times more powerful than Earth's, undergoes wild swings during each rotation.
Orbital characteristics
Neptune's elliptical, oval-shaped orbit keeps the planet an average distance from the sun of almost 2.8 billion miles (4.5 billion kilometers), or roughly 30 times as far away as Earth, making it invisible to the naked eye. Neptune goes around the sun once roughly every 165 Earth years, and completed its first orbit, since being discovered, in 2011.
Every 248 years, Pluto moves inside Neptune's orbit for 20 years or so, during which time it is closer to the sun than Neptune. Nevertheless, Neptune remains the farthest planet from the sun, since Pluto was reclassified as a dwarf planet in 2006.
Every 248 years, Pluto moves inside Neptune's orbit for 20 years or so, during which time it is closer to the sun than Neptune. Nevertheless, Neptune remains the farthest planet from the sun, since Pluto was reclassified as a dwarf planet in 2006.
Orbit & Rotation
Average Distance From The Sun
2,795,084,800 miles (4,498,252,900 km). By comparison: 30.069 times farther than Earth
Perihelion (closest approach to the sun)
2,771,087,000 miles (4,459,630,000 km). By comparison: 29.820 times that of Earth
Aphelion (farthest distance from sun)
2,819,080,000 miles (4,536,870,000 km). By comparison: 30.326 times that of Earth
Composition & structure
Atmospheric composition (by volume)
(by volume): hydrogen, 80 percent; helium, 19.0 percent; methane, 1.5 percent
Magnetic field
Roughly 27 times more powerful than Earth's
Composition
The overall composition of Neptune is, by mass, thought to be about 25 percent rock, 60 to 70 percent ice, and 5 to 15 percent hydrogen and helium, according to Tristan Guillot, author of "Interiors of Giant Planets Inside and Outside the Solar System" in the journal Science.
Internal structure
Mantle of water, ammonia and methane ices; Core of iron and magnesium-silicate
Neptune's Moons
Neptune has 14 known moons, named after lesser sea gods and nymphs from Greek mythology. The largest by far is Triton, whose discovery on Oct. 10, 1846, was in a sense enabled by beer — amateur astronomer William Lassell used the fortune he made as a brewer to finance his telescopes.
Triton is the only spherical moon of Neptune — the planet's other 13 moonsare irregularly shaped. It is also unique in being the only large moon in the solar system to circle its planet in a direction opposite to its planet's rotation — this "retrograde orbit" suggests that Triton may once have been a dwarf planet that Neptune captured rather than forming in place, according to NASA. Neptune's gravity is dragging Triton closer to the planet, meaning that millions of years from now, Triton will come close enough for gravitational forces to rip it apart.
Triton is extremely cold, with temperatures on its surface reaching about minus 391 degrees F (minus 235 degrees C), making it one of the coldest places in the solar system. Nevertheless, Voyager 2 detected geysers spewing icy matter upward more than 5 miles (8 km), showing its interior appears warm. Scientists are investigating the possibility of a subsurface ocean on the icy moon. In 2010, seasons were discovered on Triton.
In 2013, scientists working with SETI caught sight of Neptune's "lost" moon of Naiad using data from the Hubble Space Telescope.The 62-mile-wide (100 km) moon has remained unseen since Voyager 2 discovered it in 1989.
Also in 2013, scientists using the Hubble Space Telescope found the 14th moon, dubbed S/2004 N 1. It is Neptune's smallest moon and is just 11 miles (18 km) wide. It got its temporary name because it is the first satellite (S) of Neptune (N) to be found from images taken in 2004, according to NASA.
The Rings of Uranus
Neptune's unusual rings are not uniform, but possess bright thick clumps of dust called arcs. The rings are thought to be relatively young and short-lived. Earth-based observations announced in 2005 found that Neptune's rings are apparently far more unstable than previously thought, with some dwindling away rapidly, according to an article in the journal Icarus.
Research & exploration
NASA's Voyager 2 satellite was the first and as yet only spacecraft to visit Neptune on Aug. 25, 1989. The satellite discovered Neptune's rings and six of the planet's moons — Despina, Galatea, Larissa, Naiad, Proteus and Thalassa. An international team of astronomers relying on ground telescopes announced the discovery of five new moons orbiting Neptune in 200
Formation of Neptune
Neptune is generally thought to have formed with the initial buildup of a solid core followed by the capture of surrounding hydrogen and helium gas in the nebula surrounding the early sun. In this model, proto-Neptune formed over the course of 1 to 10 million years.
Need To Know
Predicted Planet
The ice giant Neptune was the first planet to be located through mathematical predictions rather than through regular observations of the sky.
The Invisible World
Want to go outside and view the planets without a telescope? You can, but you won't see Neptune. Neptune is the only planet not visible to the naked eye. This is due to the planet's extreme distance from the Earth.
Where'd It Go?
Similar to Jupiter, Neptune has storms that create gigantic spots in its atmosphere -- well, it did. When Voyager 2 flew past Neptune in 1989, it tracked and imaged the "Great Dark Spot" -- a storm larger than the entire Earth. When the Hubble Space Telescope imaged Neptune the spot had disappeared, only to be replaced with two smaller storms, which in turn also disappeared.
Wrong Way Moon
Triton, Neptune's largest moon, has a weird, backward orbit that has it inching closer to Neptune each year. When the two finally collide, the moon will be shredded into beautiful rings that may rival those of Saturn. Don't wait up, though. The collision won't occur for another 10 million to 100 million years.
Singin' Those Methane Blues
Even though it is only a small part of the atmosphere, methane gas is what gives Neptune its blue hue. Methane absorbs red light, so when we look at Neptune, all we see is the blue that is not absorbed.
Long Time
Did you know that one year on Neptune is equal to about 165 Earth years? This fact makes Neptune the planet with the longest year. 165 Earth years is a long time, especially when we consider that the planet in second place for this title (Uranus) takes only about 84 Earth years to complete its year.
No Need for Sunscreen
Neptune is so far from the sun that high noon on the big blue planet would seem like dim twilight to us. The warm light we see here on our home planet is roughly 900 times as bright as sunlight on Neptune.
Nowhere Land
Trying to land on Neptune is a really bad idea -- there's nothing to land on. Like the other three giant planets, it is a big ball of gas that gradually becomes hot liquid well below the clouds. Anyone foolish enough to drop below the cloud tops would be torn by intense winds, frozen by super cold temperatures and eventually smashed by the sheer weight of the atmosphere above, which, by the way, is poisonous to humans.
Who You Calling Little?
Even though Uranus and Neptune are much smaller than our solar system's two other giant gas planets, you could still pack nearly 60 Earths inside each. Some storms in Neptune's clouds are as big as the Earth.
Today's Forecast: Windy, Wild and Weird
Neptune is our solar system's windiest world. Winds whip clouds of frozen methane across the planet at speeds of more than 2,000 km/h (1,200 mph) -- close to the top speed of a U.S. Navy F/A-18 Hornet fighter jet. Earth's most powerful winds hit only about 400 km/h (250 mph).
In Depth
The ice giant Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. (Galileo had recorded it as a fixed star during observations with his small telescope in 1612 and 1613.) When Uranus didn't travel exactly as astronomers expected it to, a French mathematician, Urbain Joseph Le Verrier, proposed the position and mass of another as yet unknown planet that could cause the observed changes to Uranus' orbit. After being ignored by French astronomers, Le Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, its largest moon, Triton, was also discovered.
Nearly 4.5 billion kilometers (2.8 billion miles) from the Sun, Neptune orbits the Sun once every 165 years. It is invisible to the naked eye because of its extreme distance from Earth. Interestingly, the highly eccentric orbit of the dwarf planet Pluto brings Pluto inside Neptune's orbit for a 20-year period out of every 248 Earth years. Pluto can never crash into Neptune, though, because for every three laps Neptune takes around the Sun, Pluto makes two. This repeating pattern prevents close approaches of the two bodies.
The main axis of Neptune's magnetic field is tipped over by about 47 degrees compared with the planet's rotation axis. Like Uranus, whose magnetic axis is tilted about 60 degrees from the axis of rotation, Neptune's magnetosphere undergoes wild variations during each rotation because of this misalignment. The magnetic field of Neptune is about 27 times more powerful than that of Earth.
Neptune's atmosphere extends to great depths, gradually merging into water and other melted ices over a heavier, approximately Earth-size solid core. Neptune's blue color is the result of methane in the atmosphere. Uranus' blue-green color is also the result of atmospheric methane, but Neptune is a more vivid, brighter blue, so there must be an unknown component that causes the more intense color.
Despite its great distance and low energy input from the Sun, Neptune's winds can be three times stronger than Jupiter's and nine times stronger than Earth's. In 1989, Voyager 2 tracked a large, oval-shaped, dark storm in Neptune's southern hemisphere. This "Great Dark Spot" was large enough to contain the entire Earth, spun counterclockwise, and moved westward at almost 1,200 kilometers (750 miles) per hour. Subsequent images taken by the Hubble Space Telescope showed no sign of this Great Dark Spot, but did reveal the appearance and then fading of two other Great Dark Spots over the last decade. Voyager 2 also imaged clouds casting shadows on a lower cloud deck, enabling scientists to visually measure the altitude differences between the upper and lower cloud decks.
Neptune has six known rings. Voyager 2's observations confirmed that these unusual rings are not uniform but have four thick regions (clumps of dust) called arcs. The rings are thought to be relatively young and short-lived.
Neptune has 13 known moons, six of which were discovered by Voyager 2. A 14th tiny, very dim, moon was discovered in 2013 and awaits official recognition. Triton, Neptune's largest moon, orbits the planet in the opposite direction compared with the rest of the moons, suggesting that it may have been captured by Neptune in the distant past. Triton is extremely cold - temperatures on its surface are about -235 degrees Celsius (-391 degrees Fahrenheit). Despite this deep freeze at Triton, Voyager 2 discovered geysers spewing icy material upward more than 8 kilometers (5 miles). Triton's thin atmosphere, also discovered by Voyager, has been detected from Earth several times since, and is growing warmer - although scientists do not yet know why.
How Neptune Got its Name
Neptune was predicted by John Couch Adams and Urbain Le Verrier. The men independently accounted for the irregularities in the motion of Uranus by correctly predicting the orbital elements of a trans-Uranian planet. Using the predicted parameters of Le Verrier (Adams never published his predictions), Johann Galle discovered the planet in 1846. Galle wanted to name the planet for Le Verrier, but that was not acceptable to the international astronomical community. Instead, this planet is named for the Roman god of the sea.
Significant Dates
- 1846: Using mathematical calculations, astronomers discover Neptune, increasing the number of known planets to eight. Neptune's largest moon, Triton, is found the same year.
- 1984: Astronomers find evidence for the existence of a ring system around Neptune.
- 1989: Voyager 2 becomes the first and only spacecraft to visit Neptune, passing about 4,800 km (2,983 miles) above the planet's north pole.
- 1998: Scientists using telescopes on Earth and in space image Neptune's rings and ring arcs for the first time.
- 2003: Using improved observing techniques, astronomers discover five new moons orbiting Neptune.
- 2005: Scientists using the Keck Observatory image the outer rings and find that some of the ring arcs have deteriorated.
- 2011: Neptune completes its first 165-year orbit of the sun since its discovery in 1846.
- 2013: A scientist studying Neptune's ring arcs in archival Hubble Space Telescope images finds a previously unknown 14th moon of Neptune, provisionally designated S/2004 N 1.
Sources
- www.space.com
- www.nasa.gov
Note: All the information from this page is current to 2016, information can change in the future years to come
