Contents

Halimede (moon)

Moon of Neptune

Halimede

Set of stacked discovery images from August 2003, showing Halimede among trailed stars
Discovery[1][2]
Discovered by	M. Holman J. J. Kavelaars T. Grav, W. Fraser D. Milisavljevic
Discovery date	August 14, 2002
Designations
Designation	Neptune IX
Pronunciation	/hæləˈmiːdiː/[3]
Named after	Ἁλιμήδη Halimēdē
Alternative names	S/2002 N 1
Adjectives	Halimedean /ˌhæləməˈdiːən/
Orbital characteristics[4]
Epoch June 10, 2003
Semi-major axis	16,611,000 km
Eccentricity	0.2646
Orbital period (sidereal)	1879.08 d (5.14 a)
Inclination	134.1°
Physical characteristics
Mean diameter	62 km (for albedo 0.04)[5]
Albedo	0.04 (assumed)[5]
Spectral type	neutral (grey) B-V=0.73 R-V=0.35[6]

Halimede /hæləˈmiːdiː/, or Neptune IX, is a retrograde irregular satelliteofNeptune. It was discovered by Matthew J. Holman, John J. Kavelaars, Tommy Grav, Wesley C. Fraser and Dan Milisavljevic on August 14, 2002.^[7]

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.

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]

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]

Wikimedia Commons has media related to Halimede (moon).

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