Halimede (moon)

Halimede Template:IPAc-en, 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.<ref name="HolmanKavelaarsGrav2004" />

Name

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.

Orbit

File:TheIrregulars NEPTUNE GROUPS.svg

Irregular satellites of Neptune.

Halimede has the second most eccentric and third most inclined orbit around Neptune.<ref name="Williams2008-nssdc" /> 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.<ref>Template:Cite web</ref>

Physical characteristics

Halimede is about 62 kilometers in diameter (assuming an albedo of 0.04)<ref name="SheppardJewittKleyna2006" /> 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%<ref name="HolmanKavelaarsGrav2004" />) of collision in the past lifespan of the Solar System, it has been suggested that the satellite could be a fragment of Nereid.<ref name="GravHolmanFraser2004" />

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