Halimede (moon)

Halimede

Discovery
Discovered by	M.Holman JJ Kavelaars T. Grav, W. Fraser D. Milisavljevic
Discovered	August 14, 2002
Mean orbital elements
Epoch June 10, 2003
Semi-major axis	16.611 Gm
Eccentricity	0.2646
Inclination	112.712° *
Orbital period	1879.08 d (5.14 a)
Physical characteristics
Mean diameter	62 km **
Rotation period	?
Albedo	0.04 assumed
Color	neutral (grey) B-V=0.73 R-V=0.35
Spectral type	?
*to the ecliptic **based on the albedo

Irregular satellites of Neptune.

Halimede (/ˈhælᵻˈmiːdiː/ HAL-i-MEE-dee; Greek: Αλιμήδη) is a retrograde irregular satellite of Neptune. It was discovered by Matthew J. Holman et al. 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, or Neptune IX, 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.

References

• MPC: Natural Satellites Ephemeris Service
• Mean orbital parameters from JPL

External links

• Matthew Holman's Neptune's page
• David Jewitt's pages
• Neptune's Known Satellites (by Scott S. Sheppard)