Neptune is the eighth planet from the Sun and the fourth largest planet in the solar system.
It is 4.5 billion km (2.8 billion miles) from the Sun.
Neptune was visited in 1989 by a spacecraft
called Voyager 2.
Much of what we know about Neptune comes from this mission.
Neptune is one of the gas giants (along with Uranus, Saturn and Jupiter).
Its atmosphere is mostly hydrogen and helium gases.
Methane gas in the upper atmosphere
gives Neptune a beautiful blue color.
High white clouds streak the blue atmosphere.
Neptune is similar to Uranus. The two planets are also called ice giants. It has a solid core approximately the size of Earth. The core is surrounded by water and other "melted ices".
In 1989 Voyager 2 took an image of Neptune which showed a Great Dark Spot in
the southern hemisphere. The dark oval spot was a hurricane-like storm system similar to Jupiter's Great Red Spot. Another "storm" spot can be seen at the bottom of the image.
In 1994 when the Hubble Space Telescope viewed Neptune, the spots had disappeared.
But another spot was found in the planet's northern hemisphere.
Voyager 2 found several thin rings around Neptune when it flew
past the planet.
Neptune completes a rotation in 16 hours.
It takes nearly 165 Earth years for Neptune to orbit the Sun.
The dwarf planet Pluto's orbit sometimes crosses Neptune's orbit.
From 1979 to 1999 Neptune was actually farther from the Sun than Pluto was.
Now Pluto is the farthest from the Sun.
Even though Neptune is so far from the
Sun and a very very cold planet, there appears to be seasonal changes.
Since the planet takes almost 165 years to orbit the Sun, a single season
may last more than 40 years. The images
below (made over six years) show changes in the planet's southern
hemisphere.
Neptune has 13 moons, but only the largest one, Triton, can be seen from Earth.
Below is an image of what the surface of Triton might look like, with Neptune in the background.
Neptune was discovered in 1846 after astronomers realized
that an unknown object was affecting the orbit of Uranus.
They began looking for another planet and found Neptune.
The planet was named after Neptune the Roman god of the sea.
Neptune and Uranus are so similar that they are sometimes called twins.
