|Discovered||August 14, 2002|
|Mean orbital elements |
|Epoch June 10, 2003|
|Semi-major axis||16.611 Gm|
|Orbital period||1879.08 d
|Mean diameter||62 km **|
*to the ecliptic**based on the albedo
Halimede (// HAL-i-MEE-dee; Greek: Αλιμήδη), or Neptune IX, is a retrograde irregular satellite of Neptune. It was discovered by Matthew J. Holman, John J. Kavelaars, Tommy Grav, Wesley C. Fraser and Dan Milisavljevic on August 14, 2002.
Halimede has the second most eccentric and third most inclined orbit around Neptune. This is illustrated on the diagram in relation to other irregular satellites of Neptune. The satellites above the horizontal axis are prograde, the satellites beneath it are retrograde. The yellow segments extend from the pericentre to the apocentre, showing the eccentricity.
Halimede is about 62 kilometers in diameter (assuming an albedo of 0.04) and appears neutral (grey) in the visible light. Given the very similar colour of the satellite to that of Nereid together with the high probability (41%) of collision in the past lifespan of the Solar System, it has been suggested that the satellite could be a fragment of Nereid.
Halimede like many of the outer satellites of Neptune, is named after one of the Nereids, the fifty daughters of Nereus and Doris. Before the announcement of its name on February 3, 2007 (IAUC 8802), Halimede was known by the provisional designation S/2002 N 1.
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- Green, Daniel W. E. (January 13, 2003). "Satellites of Neptune". IAU Circular. 8047. Retrieved 2011-10-24.
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- Sheppard, Scott S.; Jewitt, David C.; Kleyna, Jan (2006). "A Survey for "Normal" Irregular Satellites around Neptune: Limits to Completeness". The Astronomical Journal. 132: 171–176. arXiv: . Bibcode:2006AJ....132..171S. doi:10.1086/504799.
- Grav, Tommy; Holman, Matthew J.; Fraser, Wesley C. (2004-09-20). "Photometry of Irregular Satellites of Uranus and Neptune". The Astrophysical Journal. 613 (1): L77–L80. arXiv: . Bibcode:2004ApJ...613L..77G. doi:10.1086/424997.
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- Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2011-11-03.
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