Neptune as seen from Voyager 2.
Diameter 49,528 km
30,775 mi.
Distance from the Sun 4.497 billion km
2.794 billion mi.
Astronomical Unit 30.1
Mass 1.0243×10^26 kg

17.147 Earths

Density 1.638 g/cm^3
Number of moons 14
Length of day 18 hours
Length of year 164 years
Atmosphere Components Hydrogen
Symbol Neptune symbol

Neptune is the eighth planet from the Sun, and it is the outermost major planet in our solar system. Neptune is slightly smaller but more massive (dense) than Uranus.[1][2][3][4]

Neptune is nicknamed the "Ocean Planet" because of its blue color, and no actual liquid water exists as there is on Earth. It is a gas and "ice" giant with a surface covered by crushingly dense clouds of hydrogen and helium. The outer layers are very cold: the temperature at Earth pressures are as low as -200°C (-328 °F). Near the core a water-methane mix exists at thousands of times Earth pressure, and a temperature of over 1000°C (1800°F). The winds in the atmosphere of Neptune can reach up to 1000 miles per hour (1600 kph).

One interesting speculation is that it may "rain diamonds" on Neptune, as methane breaks down into carbon and hydrogen under the heat and pressure near the core.[5]

Roman God of SeaEdit



Neptune was the Roman god of water, and a god of fertility, who was later identified with the Greek god Poseidon.

What does Neptune made of?Edit

Neptune's Great Dark Spot

Close up view of the Great Dark Spot.

Neptune consists primarily of 80% hydrogen and 19% helium. In smaller amounts, it also consists of water, methane, ammonia, and other compounds that can form ice in our solar system's temperatures.

Neptune Hurricanes

Two dark spots are visible in the picture taken by the robot Voyager 2 spacecraft in 1989: an Earth-sized Great Dark Spot located on the far left, and Dark Spot 2 located near bottom.

Neptune is classified as an ice giant planet, mainly made of the ice-forming molecules water, ammonia, and methane as a liquid mixture above what is thought to be a rocky core. Its atmosphere is mainly hydrogen and helium, along with methane gas that gives the planet a blue-green color.

Voyager 2Edit

Voyager 2 at Neptune

Voyager 2 at Neptune in Celestia.

Neptune's Bright Streak

Two hours before closest approach to Neptune in 1989, the Voyager 2 robot spacecraft snapped this picture.

In the summer of 1989, NASA's Voyager 2 became the first spacecraft to observe the planet Neptune, its final planetary target. Passing about 4,950 kilometers (3,000 miles) above Neptune's north pole, Voyager 2 made its closest approach to any planet since leaving Earth 12 years earlier. Five hours later, Voyager 2 passed about 40,000 kilometers (25,000 miles) from Neptune's largest moon, Triton, the last solid body the spacecraft will have an opportunity to study. Neptune is one of the class of planets—all of them beyond the asteroid belt—known as gas giants; the others in this class are Jupiter, Saturn and Uranus. These planets are about 4 to 12 times greater in diameter than Earth. They have no solid surfaces but possess massive atmospheres that contain substantial amounts of hydrogen and helium with traces of other gases.

Voyager 2 is one of twin spacecraft launched more than a decade ago to explore the outer solar system. Between them, these spacecraft have explored four giant planets, 48 of their moons, and their unique systems of rings and magnetic fields.

Voyager 1, launched September 5, 1977, visited Jupiter in 1979 and Saturn in 1980. It is now leaving the solar system, rising above the ecliptic plane at an angle of about 35°, at a rate of about 520 million kilometers a year.

Crescent Neptune and Triton

The picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach.

Voyager 2, launched August 20, 1977, visited Jupiter in 1979, Saturn in 1981 and Uranus in 1986 before making its closest approach to Neptune on August 25, 1989. Voyager 2 traveled 12 years at an average velocity of 19 kilometers per second (about 42,000 miles an hour) to reach Neptune, which is 30 times farther from the Sun than Earth. Voyager observed Neptune almost continuously from June to October 1989. Now Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48° and a rate of about 470 million kilometers a year.

Both spacecraft will continue to study ultraviolet sources among the stars, and their fields and particles detectors will continue to search for the boundary between the Sun's influence and interstellar space. If all goes well, we will be able to communicate with the two spacecraft for another 25 to 30 years, until their nuclear power sources can no longer supply enough electrical energy to power critical subsystems.

Moons of NeptuneEdit

Neptune and Triton

Triton (partly hidden).

Neptune has 14 moons.

  1. Naiad
  2. Thalassa
  3. Despina
  4. Galatea
  5. Larissa
  6. Hippocamp
  7. Proteus
  8. Triton
  9. Nereid
  10. Halimede
  11. Sao
  12. Laomedeia
  13. Psmathe
  14. Neso