Neptune

Heidi Hammel
Space Science Institute, Boulder, CO

One of the biggest surprises when the Voyager spacecraft flew past Neptune was a huge dark spot on the planet, and we called it the Great Dark Spot.

When we looked with the Hubble Space Telescope, that Great Dark Spot was gone. It had simply disappeared, it wasn't there any more, and that was a big surprise.

Revolution

Rotation

Radius

165 Earth years

19.1 Earth hours

24,764 km

Distance From the Sun

Mass

Density

4,498,252,900 km

102.44 x 1027 grams

1.76 gm/cm3

Mean Cloud Temperature

Moons

Atmosphere

-193 to -153C

8: Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, Nereid

hydrogen, helium, and methane

Rings

4 rings of varying lenghts believed to be relatively young and short-lived

Neptune was the first planet to be discovered due to mathematical calculations. When the orbit of Uranus did not match what it was expected to be scientists began looking for another planet which led to the discovery of Neptune in 1846.

Seasons on Neptune last 21 years.

WANT TO LEARN MORE?
Missions:
 • Voyager 2 (1977-1986)
Recent Articles:
 • Recipe for Neptune Revealed by Scientists
Additional Links:
 • JPL's Solar System Exploration
 • The Nine Planets
 • Views of the Solar System
 • Windows to the Universe