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 mostly of water, methane, and ammonia ice, with a small rocky core.
Neptune is about 30 times further away from the Sun than the Earth is. Here, the average temperature is around −200 degrees C. It is so far away that it is the only planet we cannot see from Earth without the help of a telescope.
The planet is about four times as wide as the Earth. It is also tilted on its axis by about the same amount as the Earth. This means that the planet has seasons as 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 an unusual 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. Neptune is so far away from the Sun that, since its discovery, it has completed only one full orbit. Each orbit takes 165 years.
Neptune has an atmosphere made mainly of hydrogen and helium. It also has the fastest known winds on any planet, with speeds of around 2,000 km per hour.
The only spacecraft to visit Neptune was Voyager 2 in 1989. This means there is still a lot we do not know about the planet. For example, scientists are still studying what gives Neptune its bright blue colour.
- Moons
We know that Neptune has at least 14 moons. They are all named after water gods or sea creatures from Greek and Roman mythology.
The largest moon is called Triton. It was discovered only 17 days after Neptune in 1846. Triton is large enough to have its own thin atmosphere. Scientists think Triton was moving past Neptune when the Solar System was still forming. It was then captured by Neptune’s gravity and became a moon.
Most moons form from material left behind as the planet itself forms. Scientists think that when Triton was captured, it made some other moons unstable. These moons may have crashed into each other, breaking into small pieces. These pieces now make up the ring system we see around Neptune today.
Psamathe and Neso are two of Neptune’s other moons. They orbit further away from Neptune than any other moons 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 one hundredth of Triton’s mass.
Image
CreditThis work by NASA is licensed under Creative Commons Zero v1.0 UniversalImage of Triton, taken in 1989 by Voyager 2