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 -153°C	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.

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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