Image of Nereid taken by Voyager 2
|Date of discovery||May 1, 1949|
|Name of discoverer||Gerard P. Kuiper|
|Name origin||Any of fifty women, daughters of Nereus and Doris, who attended Neptune|
|Order from primary||8|
|Semi-major axis||5,513,400 km|
|Sidereal month||360.13619 da|
|Avg. orbital speed||1.12 km/s|
|Inclination||27.6° to Neptune's equator|
|Sidereal day||11.52 hr|
|Rotational speed||0.02576 km/s|
|Mass||3.09 * 1019 kg|
|Mean radius||170 km|
|Surface gravity||0.713 m/s²|
|Escape speed||0.156 km/s|
|Surface area||363,158 km²|
|Composition||Ice and silicates|
Discovery and naming
Nereid is in a highly eccentric orbit around Neptune, and in fact its orbit is the most eccentric orbit of any solar system body. Its sidereal month is about 360.14 Julian days. Nereid's orbit is inclined about 28 degrees from Neptune's equator, but is inclined only 7.23 degrees from the local Laplace plane. Almost no astronomer believes that Nereid formed with the planet, and most astronomers believe that Nereid is a captured Kuiper belt or other trans-Neptunian object.
Nereid has a mass of 3.09 * 1019 kg, the third greatest mass of the moons of Neptune. Its color is neutral-gray. Another moon of Neptune, Halimede (formerly S/2002 N 1), has the same neutral color, leading some astronomers to suggest that Halimede is a fragment of Nereid broken off in a collision with another, unknown object.
Observation and Exploration
Telescopic observation has revealed little about Nereid beyond its orbital elements. The one spacecraft that visited the Neptunian system, Voyager 2, captured one low-resolution image of Nereid but did not fly close enough to it to discover more.
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Nine8 Planets, May 6, 1995. Accessed June 8, 2008.
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