Neptune is the furthest planet from the Sun. About 30 times further away than the Earth is. It is a blue giant planet like Uranus.
These planets are also called ice giants. They are made of mostly water, methane and ammonia ice, with a small rocky core.
Neptune is about 30 times further away form the Sun than the Earth is. Here the average temperature is -200 degrees C. It is so far away that it is the only planet we can't see from Earth without the help of a telescope.
The planet is about 4 times as wide as the Earth. It is also titled on its axis, by about the same amount as the Earth. This means that the planet has seasons like we do - but each one on Neptune lasts over 40 years!
Neptune's existence was predicted before it was ever seen. Astronomers noticed that the nearby planet, Uranus, seemed to have a strange orbit. It looked like Uranus was being pulled by another planet. Scientists used maths to predict where the planet should be, and in 1846 it was discovered. It is so far away from the Sun that since it's discovery it has only completed one full orbit, each taking 165 years!
Neptune has an atmosphere made of mainly hydrogen and helium. It also has the fastest known winds on any planet, with speeds of around 2000 km per hour.
The only spacecraft to visit Neptune was Voyager 2 in 1989. This means there is still a lot we don't know about the planet. For example, what gives it such a bright blue colour?
- Moons
We know that Neptune has at least 14 moons. They are all named after water gods or creatures in Greek and Roman mythology.
The largest of the moons is called Triton (the Greek god of the sea). It was found only 17 days after the planet was discovered in 1846. Triton is big enough to have its own thin atmosphere. It is thought that Triton was passing by Neptune when the Solar System was still forming. It was then captured by Neptune's gravity and became a moon. Most moons are made from the debris left as the planet itself formed. We think that when Triton was captured it made some other moons orbiting around Neptune unstable. These then crashed into each other breaking into tiny pieces. These make the ring system we see around Neptune today.
Psamathe and Neso are 2 of Neptune's other moons. They orbit further away from their planet than any other moon in the Solar System. Apart from Triton, Neptune's moons are all very small. If you added them all together they would not even make 1/100th of the mass of Triton!
Image
CreditThis work by NASA is licensed under Creative Commons Zero v1.0 UniversalImage of Triton, taken in 1989 by Voyager 2