Halimede (moon)


Set of stacked discovery images from August 2003, showing Halimede among trailed stars
Discovered by
Discovery dateAugust 14, 2002
Neptune IX
Named after
Ἁλιμήδη Halimēdē
S/2002 N 1
AdjectivesHalimedean /ˌhæləməˈdən/
Orbital characteristics[4]
Epoch June 10, 2003
16,611,000 km
1879.08 d
(5.14 a)
Physical characteristics
Mean diameter
62 km (for albedo 0.04)[5]
Albedo0.04 (assumed)[5]
Spectral type
neutral (grey)
B-V=0.73 R-V=0.35[6]

Halimede /hæləˈmd/, 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.[7]


Halimede imaged by the Very Large Telescope during follow-up observations on 3 September 2002

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.


Irregular satellites of Neptune.

Halimede has the second most eccentric and third most inclined orbit around Neptune.[8] 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. It is also worth mentioning that Sao and Laomedeia are similar to Halimede but they both have prograde orbits unlike Halimede which has a retrograde orbit.[9]

Physical characteristics

Halimede is about 62 kilometers in diameter (assuming an albedo of 0.04)[5] 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%[7]) of collision in the past lifespan of the Solar System, it has been suggested that the satellite could be a fragment of Nereid.[6]


  1. ^ JPL (2011-07-21). "Planetary Satellite Discovery Circumstances". Jet Propulsion Laboratory. Retrieved 2011-10-24.
  2. ^ Green, Daniel W. E. (January 13, 2003). "Satellites of Neptune". IAU Circular. 8047. Retrieved 2011-10-24.
  3. ^ Noah Webster (1884) A Practical Dictionary of the English Language
  4. ^ Jacobson, R. A. (2008). "NEP078 – JPL satellite ephemeris". Planetary Satellite Mean Orbital Parameters. Retrieved 2009-09-23.
  5. ^ a b c Sheppard, Scott S.; Jewitt, David C.; Kleyna, Jan (2006). "A Survey for "Normal" Irregular Satellites around Neptune: Limits to Completeness". The Astronomical Journal. 132 (1): 171–176. arXiv:astro-ph/0604552. Bibcode:2006AJ....132..171S. doi:10.1086/504799. S2CID 154011.
  6. ^ a b 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:astro-ph/0405605. Bibcode:2004ApJ...613L..77G. doi:10.1086/424997. S2CID 15706906.
  7. ^ a b Holman, M. J.; Kavelaars, J. J.; Grav, T.; et al. (2004). "Discovery of five irregular moons of Neptune" (PDF). Nature. 430 (7002): 865–867. Bibcode:2004Natur.430..865H. doi:10.1038/nature02832. PMID 15318214. S2CID 4412380. Retrieved 24 October 2011.
  8. ^ Williams, Dr. David R. (2008-01-22). "Neptunian Satellite Fact Sheet". NASA (National Space Science Data Center). Retrieved 2011-11-03.
  9. ^ "In Depth | Halimede". NASA Solar System Exploration. Retrieved 2020-11-10.

External links

  • Matthew Holman's Neptune's page
  • David Jewitt's pages
  • Neptune's Known Satellites (by Scott S. Sheppard)
  • MPC: Natural Satellites Ephemeris Service
  • Mean orbital parameters from JPL