Neptune

Neptune is the eighth farthest planet from the Sun with dark, cold and whipped by supersonic winds. The ice giant is 30 times as far as the Sun from Earth and is the only planet not visible with the naked eye. Since its discovery in 1846, Neptune has completed its first 165-year orbit.

High noon on Neptune would look like dim twilight to us since the ice giant is so far from the Sun. The warm light as seen here on Earth is 900 times brighter as sunlight on Neptune.

Neptune was the first planet to be discovered with mathematical equations. Johann Galle discovered the planet in 1846, with help from Urbain Le Verrier's calculations.

Size and Distance
Neptune is about 4 times wider than Earth, with a radius of 15,299.4 miles (24,622 kilometres). Neptune would be the size of a basketball if Earth was the size of a nickel.

Neptune is 30 astronomical units away from the Sun with an average distance of 2.8 billion miles (4.5 billion kilometres). One astronomical unit (abbreviated as 'AU') is the equal distance from the Sun to the Earth. Sunlight takes 4 hours to travel to Neptune from this distance.

Orbit and Rotation
One day on Neptune lasts 16 hours (the time it takes for Neptune to complete 1 rotation). Neptune makes a complete orbit around the Sun (a year in Neptunian time) in about 165 Earth years (60,190 Earth days).

Neptune can sometimes be farther away from the Sun than dwarf planet Pluto. Pluto's oval shape brings it inside Neptune's orbit for a 20 year period every 248 Earth years. This switch happened most recently from 1979 to 1999. Pluto could never crash into Neptune because for every 3 laps Neptune takes around the Sun, Pluto makes 2. This repeating pattern prevents close approaches with the two planets.

Neptune is tilted at 28 degrees which is similar to Mars' and Earth's tilt. This means that Neptune experiences seasons like Earth; however, each season lasts 40 years.

Structure
Neptune is one of two ice giants in the outer solar system (the other being Uranus. Most of the planet's mass (80%) is made up of hot dense "icy" materials - water, methane and ammonia - above a small rocky core. Neptune is the densest planet out of the two ice giants.

Scientists theorize that there could be a super hot water ocean under Neptune's cold clouds. It doesn't boil away because the extreme pressures keep it locked inside.

Formation
When the rest of the solar system settled into its current, about 4.5 billion years ago, Neptune was formed when swirling gas and dust were pulled together to create this ice giant. Like Uranus, Neptune likely formed closer to the Sun but moved to the outer solar system over time.

Surface
Neptune does not have a true solid surface. It's atmosphere (mostly composed of hydrogen, helium and methane) extends to great depths gradually merging into water and other melted ices over a heavier, solid core that measures in the same mass as Earth.

Atmosphere
Neptune's atmosphere is mostly composed of hydrogen, helium and methane. Uranus has a blue-green colour due to the abundance of methane, but Neptune gives us a vivid, brighter blue, which must mean there is a more stronger component in Neptune's atmosphere that causes this intense colour.

Neptune has the highest wind speeds in our solar system. Despite great distance and low sunlight, Neptune's winds can be three times stronger than Jupiter's and nine times stronger than Earth's. These speedy clouds, composed of frozen methane, can reach up to more than 1,200 miles per hour (2,000 kilometres per hour). Even Earth's most powerful wind speeds can only reach up 250 miles per hour (400 kilometres per hour).

In 1989, a large, oval shaped storm was given the name the "Great Dark Spot" that was large enough to fit one Earth in it. That storm has since faded, but new ones have appeared on different parts of the planet.

Magnetosphere
Neptune's magnetic field axis is tipped over by 47 degrees compared with the planet's rotation axis. Like Uranus, whose magnetic field is tilted 60 degrees on its axis, Neptune's atmosphere undergoes various changes during each rotation due to the misalignment.

Rings
Neptune has at least five main rings and four prominent ring arcs that we know of so far. Starting at the planet and moving outwards, the main rings are named Galle, Leverrier, Lassell, Arago and Adams. The rings are theorized to be young and short-lived.

Neptune's inner ring system also has peculiar clumps of dust called arcs which are named Liberté (Liberty), Egalité (Equality), Fraternité (Fraternity) and Courage. These located in the outermost ring, Adams. The arcs are strange because the laws of motion would predict that they would be spread out evenly rather than being clumped together.

Moons
Neptune has 14 moons in orbit, the largest currently being Triton which was discovered on October 10, 1846, by William Lassell 17 days after the original planet was discovered. since Neptune was named after the Roman god of the sea, its moons were named after various sea gods and nymphs in Greek mythology.

Triton is the only large moon in our solar system that circles its planet in the opposite direction to the planet's rotation (a retrograde orbit). This suggests that Triton may have been a captured, independent object in Neptune's orbit. Triton is extremely cold, with surface temperatures that reach up to -235 degrees celsius. Voyager 2, despite the deep freeze on this moon, captured geysers spewing icy material upwards to more than 5 miles (8 kilometres). Triton's thin atmosphere, also discovered by Voyager spacecrafts, has been detected from Earth several times since, but scientists don't know why.

<More on Neptune's Moons

Human Life
Neptune's extreme temperatures and pressure make human life very unlikely to colonise on this planet.