What's the eighth planet from the Sun — the one that's big, blue, cold and buffeted by supersonic winds? If you didn't immediately come up with the answer "Neptune," don't feel too bad. The outermost of the four gas giants — a category that also includes Jupiter, Saturn and Uranus — isn't a celestial object that most of us think much about, in part because it's so far away that it can't be seen with the unaided eye.
Though Neptune was discovered back in 1846 by German astronomer Johann Gottfried Galle, scientists didn't know all that much about the planet until the Voyager 2 probe did a flyby in 1989, which resulted in the first close-up photos of Neptune and a wealth of other information. Pluto's recent demotion to dwarf planet status gives Neptune added significance, in that at 2.8 billion miles (4.5 billion kilometers) from the sun, it's now the most distant of the true planets in the solar system, according to NASA.
Here are 10 of the more interesting facts about the faraway behemoth.
10: Neptune Almost Was Named "Le Verrier."
When the Italian astronomer Galileo first glimpsed Neptune through a small telescope in 1612 and 1613, he marked it down in his charts as a star. It wasn't until the late 1830s that a French astronomer, Urbain Jean Joseph Le Verrier, charted an odd irregularity in the orbit of Uranus, which at that time was the most distant planet that had been discovered. Le Verrier figured out that Uranus's path was being influenced by the presence of another unknown planet, and calculated the precise location in the heavens where he thought it would be found. Using that information, Johann Gottfried Galle, an astronomer at the Berlin observatory, needed only a single night of searching to discover the new planet in 1846.
Galle wanted to name the planet after Le Verrier, but the international astronomical community apparently didn't believe in naming planets after anyone but Greco-Roman mythological figures. So, the new planet was named for Neptune, the Roman god of the sea. A century and a half later, when close-up photos of the planet showed it to be a brilliant, ocean-like vivid blue, the name suddenly seemed more appropriate.
9: A Year on Neptune Is a Long Time.
Because Neptune is so far from the sun, it takes a long, long time for it to complete an orbit. The Neptunian year lasts the equivalent of 164.79 Earth years, which means that only one year has passed on the distant planet since it was discovered in 1846. Neptune tilts on its axis at 28.3 degrees, a similar angle to Earth. For half of its year, its north pole is tilted toward the sun, while its south pole is tilted in that direction during the other half. Like the Earth, Neptune has seasons, but they're extremely long by our standard; summer, for example, lasts 41 years.
8: In Certain Regions of Neptune, the Length of the Day Varies by as Much as Six Hours.
Like the other giant gas planets, Neptune doesn't have a solid surface. That allows different regions of the planet to rotate at different speeds. At the equator, Neptune completes a rotation in 18 hours, while near the poles, the day is just 12 hours long. This phenomenon is called "differential rotation," and Neptune has the most extreme differential of the four gas giants.
7: Like Saturn, Neptune Has Rings.
Astronomers first found evidence that Neptune had a ring system in 1984, but it wasn't until 1998 that they combined data from terrestrial and space telescopes to image Neptune's rings for the first time. They're not uniform, but are composed of four thick regions, and are made of dust, according to NASA. The planet has six known rings, which are named Liberty, Equality, Fraternity, Adams, Leverrier and Arago.
6: Neptune Has a Lot of Moons.
Voyager 2 discovered six previously unknown moons orbiting Neptune, giving it at least 13 natural satellites. Triton, the biggest moon, orbits the planet in the opposite direction of the rest of the moons, which scientists say means it may have been captured by Neptune in the distant past. Triton is really, really cold; the temperature on its surface is about minus 391 degrees Fahrenheit (minus 235 degrees Celsius). Voyager 2 spotted geysers on Triton's surface, spewing jets of icy material 5 miles (8 kilometers) into its thin atmosphere. Triton's atmosphere, oddly, seems to be getting warmer, though scientists don't know why.
5: Nobody Knows Why Neptune Is Such a Vivid Shade of Blue.
The blueness of Neptune comes from the methane in its atmosphere. But that doesn't explain why it's such a brilliant shade of blue, compared to, say, Uranus, which also has a lot of methane in its atmosphere, but is more of a blue-green hue. Scientists suspect that Neptune's peculiar blueness is caused by some yet-unknown component of its atmosphere.
4: Neptune Has Really, Really Nasty Weather.
For a planet that's so far from the sun and receives so little solar energy, Neptune has really, really energetic weather. Its winds are three times stronger than Jupiter's and nine times stronger than those on Earth, according to NASA. And its storm systems are monstrous. In 1989, for example, Voyager 2 tracked an oval-shaped, counterclockwise cyclone in Neptune's southern hemisphere, dubbed the Great Dark Spot, which was big enough to contain the entire Earth. The giant storm moved westward at a speed of 750 miles per hour (1,200 kilometers per hour).
3: If There Were Radio Stations on Neptune, the Reception Would Be Pretty Bad.
Neptune's magnetic field is 27 times more powerful than the Earth's, according to NASA, and its polarity is reversed. But that's only part of the difference between Neptune's and Earth's magnetism. Compared to Neptune's rotational axis, the main axis of its magnetic field is tipped by about 47 degrees. This misalignment causes Neptune's magnetosphere to undergo dramatic variations in the course of the Neptunian day, as the planet rotates in the solar wind (that is, the stream of charged particles ejected from the Sun).
Of course, since Neptune has no inhabitants, the potential effect of all that magnetic weirdness on radio transmissions is kind of moot. But Neptune's magnetic field does produce other strange phenomena. For example, the giant planet has auroras, similar to the northern and southern lights on Earth, which are caused when energetic particles strike the Earth's atmosphere and spiral down the magnetic field lines near the poles. But because Neptune's magnetic field is so complex, the auroras occur over wide regions of the giant planet, not just at the poles, according to NASA.
2: It Would Take a Long Time to Get to Neptune.
We're not sure why you would want to go there, since its methane-laden atmosphere, intense gravity and non-solid surface would make landing inadvisable. And besides, the 5.6-billion-mile (9-billion-kilometer) round trip would take up a good portion of your life, if you survived the journey. Voyager 2, the robotic probe that became the first (and so far, the only) Earth spacecraft to reach Neptune, took 12 years to get there. Voyager 2 flew about 3,000 miles (4,828 kilometers) above Neptune's north pole, the closest approach that it made to any of the planets, and then got to within 25,000 miles (40,000 kilometers) of Neptune's largest moon, Triton, according to NASA. Unlike human astronauts, there wasn't any worry about getting Voyager back to Earth in one piece. After visiting the eighth and outermost planet, the probe simply continued on its journey out of the solar system.
1: Neptune May Be a Giant Diamond and Oil Factory.
A 1999 study by University of California-Berkeley scientists simulated the atmospheric pressures of the gas giants Neptune and Saturn, which are believed to be 100,000 to 500,000 times that of the Earth's. When subjected to that intense of a squeeze, the scientists found that Neptune's methane would decompose, with some of the hydrogen atoms breaking away and leaving the carbon to be compressed into pure, tiny diamonds. The remaining hydrogen and carbon atoms chained into hydrocarbons, similar — though not quite identical — to the petroleum pumped from underground deposits on Earth, according to Reuters.