Lissauer, Jack J. Space Science and Astrobiology Division, Planetary Systems Branch, Ames Research Center, National Aeronautics and Space Administration, Moffett Field, California.
Marley, Mark S. Space Science and Astrobiology Division, Planetary Systems Branch, Ames Research Center, National Aeronautics and Space Administration, Moffett Field, California.
Last reviewed:February 2019
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- Magnetic field
- Origin and evolution
- Related Primary Literature
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The eighth planet in order of distance from the Sun and the outermost of the four giant planets in our solar system. Most of what is known about Neptune is the result of the flyby of the planet by Voyager 2 in August 1989, after the space probe had visited Uranus in 1986. The spacecraft discovered that Neptune has a ring system and gathered detailed images of the planet and its moons, including Triton, the seventh largest moon in the solar system. Overall, the Voyager results confirmed that Neptune (Fig. 1) is a near twin of Uranus in size, mass, and composition. With atmospheres and interiors that are strongly enriched in heavy elements, yet less massive than the gas giants Jupiter and Saturn, Neptune and Uranus make up a separate type of planet commonly termed "ice giants." Many planets of similar masses have been found in exoplanetary systems. Neptune and Uranus enable important case studies that help in understanding this common class of world. See Table 1 for planetary and orbital characteristics of Neptune. See also: Exoplanet; Jupiter; Planet; Saturn; Solar system; Space probe; Uranus
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