Neptune

Neptune is very similar to Uranus, but it is slightly smaller in diameter and more massive.

Facts about Uranus

• Wind speeds on Neptune can reach 450 meters per second.
• Neptune was discovered because its gravitational field was affecting the orbit of Uranus.
• Neptune is sometimes the ninth planet from the Sun.

How big is Neptune

Neptune has a diameter of 49,528 km across at the equator and 48,681 km from pole to pole. It is almost as big as four Earths in a row. It bulges out a little at the equator because of its rotation, but not as much as Jupiter and Saturn.

What is Neptune's surface like?

Neptune is a gas giant so it does not have a surface that you can stand on without going deep into its atmosphere. The atmosphere looks blue-green. It has some dark blue spots. When the Voyager probe went by Neptune in 1989, there was a large one called the Great Dark Spot. Now it is gone and there are new spots. There are some high white clouds too. The winds of Neptune are very fast, blowing at up to 2000 km per hour. That is about ten times faster than the winds of some of Earth's strongest tornadoes.

What are Neptune's rings like?

Neptune has some faint rings that are dark and hard to see. There are clumps in some parts of the rings where the material is more dense. It could be because of the gravity of the nearby small inner moons of Neptune.

What are Neptune's moons like?

Neptune has 13 known moons. There could be more.

Inner moons

There are five small potato shaped moons orbiting close to Neptune.

Proteus

Proteus is a dark moon about 420 km across. It is irregularly shaped, but it is almost big enough for its gravity to pull it into a sphere. In Roman mythology Proteus was Neptune's herdman who could change into any shape he wanted.

Triton

Triton is the largest moon of Neptune. Scientists think that it is a lot like Pluto. It is 2700 km across. It is made of rock and some water ice. It has a surface temperature of −236 °C making it the coldest world visited by spacecraft. Triton has a very thin atmosphere made up nitrogen and a little methane.

There are volcanoes that have eruptions of liquid nitrogen, dust, or methane compounds. The eruptions happen because of the seasons. They make plumes up to 8 km high. There are few craters because the eruptions cover them up. There are ice caps of nitrogen and methane ice that change sizes with the seasons. There are also ridges and valleys. They may have formed because the changing seasons caused the material to repeatly freeze and warm up.

An interesting thing about Triton's orbit is that it goes around Neptune in the opposite direction from the direction of Neptune's rotation. Because of that, scientists think that Triton was captured by Neptune long ago. Its orbit is also very circular. Neptune's gravity made the orbit circular over a long time after the capture. The tidal effects involved in that may have heated Triton and kept ices melted for a billion years. In Roman mythology, Triton was the son of Neptune.

Nereid

Nereid is an irregularly shaped moon about 340 km across. Its orbit is very eccentric or noncircular. It may have been captured by Neptune or moved into the eccentric orbit by Triton's gravity when Triton got captured. In Roman mythology nereids were sea nymphs.

Outer moons

There are five other known moons. They are small potateo-shaped moons far from Neptune. There could be more yet to be discovered.

How long is a day on on Neptune

A day on Neptune lasts 16 hour and 7 minutes.

What is Neptune made of?

Neptune is made of rock and metal in the core. The core is probably bigger than Uranus's because Neptune weighs more, but is the same size. Around the core is rock, water, ammonia and methane. The atmosphere makes up most of the planet and is made of hydrogen and helium. Lower down in the atmosphere, there is methane and ammonia too. The methane makes Neptune look blue- green.

What is Neptune made of?

Neptune is made of rock and metal in the core. The core is probably bigger than Uranus's because Neptune weighs more, but is the same size. Around the core is rock, water, ammonia and methane. The atmosphere makes up most of the planet and is made of hydrogen and helium. Lower down in the atmosphere, there is methane and ammonia too. The methane makes Neptune look blue- green.

How much would I weigh on Neptune?

Neptune's rotation is not as rapid as that of Jupiter and Saturn. That means its equator does not bulge out as much. So, Neptune's rotation would not cancel out as much of its gravity's force.

Who is Neptune named after?

Neptune is named after the Roman god of the seas, also known as Poseidon in ancient Greece.