# Wikijunior:Solar System/Neptune

!Neptune as seen from Voyager
2
{{/Coolfacts\|=
1\|!♆.svg "♆"){width="80"}\|= 2\|Neptune
Facts:\|= 3\|\*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 farther from the Sun than Pluto.

}}

## How big is this planet ?

{{  }} !Comparison of the size of Neptune
and the
Earth
Neptune is very similar to Uranus in size. Its diameter is only slightly
smaller, at 49,528 km wide. [^1] It is almost as big as four Earths in
length.[^2]

## What is its surface like?

The **atmosphere** of Neptune has some dark blue spots. When the Voyager
probe went by Neptune in 1989, it saw a large one called the Great Dark
Spot. In 1994, it vanished, but later reappeared.[^3] There is also a
large white cloud nicknamed \"Scooter.\" It goes around Neptune every 16
hours.[^4] The winds of Neptune are very fast, blowing at up to 2000 km
per hour(the fastest in the entire solar system).[^5] That is about four
times faster than the fastest recorded tornado on Earth.

## What are its 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 **denser**.[^6]

## What are its moons like?

Neptune has 13 moons. There could be more.[^7]

### Inner Moons

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

#### Proteus

Proteus is a dark moon about 418 km across. It has an irregular shape.
In Roman mythology Proteus was a sea-god who could change into any shape
he wanted.[^8]

#### 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 ice. It has a
surface temperature of −235 °C Triton has a very thin atmosphere made up
of **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. There
are few **craters** because the eruptions cover them up. There are ice
caps that change sizes with the seasons. There are also **ridges** and
**valleys**. They may have formed because of repeated freezing and
thawing.

An interesting thing about Triton\'s orbit is that it goes around
Neptune in the opposite direction that Neptune\'s rotates. Because of
this, scientists think that Triton was captured by Neptune long ago. In
Roman mythology, Triton was the son of Neptune.[^9]

#### 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.[^10]

### Outer Moons

There are five other known moons. They are small potato-shaped moons far
from Neptune. There might be more we haven\'t seen yet.

## How long is a day on this planet?

A day on Neptune lasts 16 hours and 7 minutes.[^11]

## How long is a year on this planet?

One year on Neptune is about 165 Earth years, or 60,265 days.[^12]

## What is it 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 is made of **hydrogen** and **helium**. Lower down in the
atmosphere, there is methane and ammonia too. The methane makes Neptune
look blue-green.[^13] !Artistic impression of the mythological
Neptune.jpg "Artistic impression of the mythological Neptune")

## How much would Neptune\'s gravity pull on me?

If you were floating close to the cloud tops of Neptune, it would pull
you down with a force only a little stronger than the force of Earth\'s
gravity.[^14] The effects of Neptune\'s larger **radius** and its
**mass** almost cancel out, making the force only a little bigger.

## Who is it named after?

Neptune is named after the Roman god of the seas, also known as Poseidon
in ancient Greece. [^15]

Next Topic: Pluto

## References

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<references/>
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Sonnensystem/ Neptun
nl:Wikijunior:Zonnestelsel/Neptunus
pl:Wikijunior:Układ_Słoneczny/Neptun

[^1]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^2]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html>

[^3]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^4]: <http://www.nineplanets.org/neptune.html>;
    <http://www.moreheadplanetarium.org/index.cfm?fuseaction=page&filename=science_resources_neptune.html>

[^5]: <http://www.nineplanets.org/neptune.html>;
    <http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level1/neptune.html>

[^6]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^7]: <http://www.nineplanets.org/neptune.html>

[^8]: <http://www.nineplanets.org/proteus.html>

[^9]: <http://www.nineplanets.org/triton.html>

[^10]: <http://www.nineplanets.org/nereid.html>

[^11]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^12]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html>;
    Smith, Bradford A. \"Neptune.\" World Book Online Reference Center.
    2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^13]: <http://www.nineplanets.org/neptune.html>;
    Smith, Bradford A. \"Neptune.\" World Book Online Reference Center.
    2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^14]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 281. West Publishing
    Company. 

[^15]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 282. West Publishing
    Company. 
