Glossary term: Neptune

Description: Neptune is the eighth, and farthest, major planet from the Sun. Like its neighbor Uranus, Neptune is an ice giant. Neptune's radius is a little less than four times Earth's radius and it has no firm surface. Neptune has a solid rock core surrounded by a layer of high-pressure water, methane, and ammonia. In the early outer Solar System these chemicals were frozen and accreted onto the young Neptune, hence the name "ice giant". Neptune's outer atmosphere is a thick, puffy layer of hydrogen and helium. Neptune has at least 14 moons and a faint ring system. As the outermost major planet, Neptune's gravity plays a pivotal role in shaping the orbits of smaller bodies in the Kuiper Belt.

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Neptune is spherical and blue with thin bands of white cloud and a slightly darker spot just below its equator


Caption: Voyager 2 Narrow Angle Camera image of Neptune taken in August 1989. The Great Dark Spot, flanked by cirrus clouds, is at center. A smaller dark storm, Dark Spot Jr., is rotating into view at bottom left. Additionally, a patch of white cirrus clouds to its north, named "Scooter" for its rapid motion relative to other features, is visible.
Credit: NASA / JPL / Voyager-ISS / Justin Cowart credit link
License: PD Public Domain icons