Space and Time
Size: Diameter 49,532km
Mass: 1.024x10(exp26)kg
Composition: Rock, ice core
Mean temperature: -220°c
Distance from Sun: 4504 million km
Atmosphere/weather: Hydrogen, helium and methane
Moon/satellites: 8
Orbital length: 60,190.3 days
Length of day: 16 hours 7 minutes
Distance from Earth: Max 4,564 million km, min 4,354 million km
The eighth planet from the Sun, Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. When Uranus didn't travel exactly as astronomers expected it to, two mathematicians, working independently of each other, proposed the position and mass of another, as yet unknown planet that could account for Uranus' orbit. Although many ignored the predictions, a young astronomer decided to look for the predicted planet. Thus, Neptune was discovered in 1846. Seventeen days later, its largest moon, Triton, was also discovered.
Neptune orbits the Sun once every 165 years and so has not quite made a full circle around the Sun since it was discovered. It is invisible to the naked eye because of its extreme distance from Earth. Because of Pluto's unusual elliptical orbit, Neptune is actually the farthest planet from the Sun for a 20-year period out of every 248 Earth years. |
Clouds seen high in Neptune's atmosphere. Its blue colour is due to high amounts of methane
Neptune has the smallest diameter of our solar system's giant gas planets (including Jupiter, Saturn and Uranus), so called because they have no solid surfaces. Even so, its volume could hold nearly 60 Earths. Neptune's atmosphere extends to great depths, gradually merging into water and other 'melted ices' over a heavier, approximately Earth-sized liquid core. Neptune's rotational axis is tilted 30 degrees to the plane of its orbit around the Sun. Its seasons last an incredible 41 years. During the southern summer, the south pole is in constant sunlight for about 41 years and in northern summer, the north pole is in constant sunlight for about 41 years.
See Neptune rotate in this Hubble Space Telescope image loop of real data. Courtesy of the Hubble Space Telescope Science Institute and the Associated Universities for Research in Astronomy under contract to NASA. Original videos may be found at the Space Telescope Science Institute.
A close up view of Neptune's largest moon, Triton
Neptune's atmosphere is made up of hydrogen, helium, and methane, the last of these giving the planet its blue colour (because methane absorbs red light). Despite its great distance from the Sun and lower energy input, Neptune's winds are three times stronger than Jupiter's and nine times stronger than Earth's.
The planet has several rings of varying widths. Neptune's rings are believed to be relatively young and relatively short-lived.
Neptune has 11 known moons, six of which were discovered by the Voyager 2 spacecraft which visited the planet in 1989. The largest, Triton, orbits Neptune in a direction opposite to the planet's rotation direction. It is gradually getting closer until it will collide with the planet in about 10 to 100 million years, forming vast rings around Neptune. These will rival or exceed Saturn's extensive ring system. Triton is the coldest body yet visited in our solar system. Temperatures on its surface are about -235 C. Despite the deep freeze, Voyager 2 discovered great geysers of gaseous nitrogen on Triton.
In Roman mythology Neptune (in Greek known as Poseidon) was the god of the sea.
Images, information and videos courtesy of NASA.