Neptune

Neptune is the ninth planet in the Solar System and the outer twin of Uranus. It is a slightly smaller version of Uranus, but shows more weather activity. Neptune and Uranus are smaller giant planets than Saturn and Jupiter, have an atmosphere made of methane, ammonia, hydrogen and helium, a mantle of rock and ice and a core of rock. This gives them the nickname ice giants.

Structure
Neptune is made of an atmosphere of ammonia and methane. Beneath the atmosphere is the surface (mantle). The mantle is hot because underneath it lies a small core the size of Earth which has a temperature of 5000°C. The core is so hot that it creates more convection than the Uranian.

Storms and weather activity
Storms on Neptune have been observed since 1989, when Voyager 2 flew by the planet. It discovered a large storm the size of Asia, the Great Dark Spot. It was similar to Jupiter's Great Red Spot but dissipated by 1994. Another notable weather feature is the Scooter, a high-speed storm which rotated around the planet at winds of 2,100 km/h, much faster than the Great Dark Spot. When the GDS dissipated, a new storm had quickly formed and was named the Small Dark Spot, or the Wizards Eye, but also dissapeared in 1994. So Neptune is a stormy world compared to Uranus.

Moons
Triton is Neptune's largest moon. It is a rocky world with a temperature of -230°C, but has lots of geysers. How could geysers form at such freezing temperatures? Scientists think that the heat to create geysers comes from tidal heating from Neptune. Nereid is also a major moon, but it is more far away at a distance of 5,513,787 km (0.3685 AU).