Halimede (moon)

Matthew J. Holman et al.

Halimede ( Neptune IX ) is the zehntinnerste innermost and the outer retrograde irregular moons of the planet Neptune. He is probably caused by a collision of Neptune's moon Nereid 's third largest with another body.

Discovery and designation

Halimede was on 14 August 2002 by a team consisting of Matthew J. Holman, John J. Kavelaars, Tommy Grav, Brett J. Gladman, Wesley C. Fraser, Dan Milisavljevic, Philip D. Nicholson, Joseph A. Burns, Valerio Carruba, Jean -Marc Petit, Philippe Rousselot, Oliver Mousis, Brian G. Marsden and Robert A. Jacobson on recordings from 14 August to 4 September 2002, and on 10 August 2001 discovered along with Sao and Laomedeia. The recordings were made by the 4.0 -meter Blanco telescope at the Cerro Tololo Inter- American Observatory in Chile, and the 3.6 -meter Canada -France - Hawaii Telescope in Hawaii. Several recordings were digitally combined until the moons as opposed to the line-shaped stars appeared point-like. The discovery was announced on 13 January 2003; the moon first received the provisional designation S/2002 N 1

On 3 February 2007, the moon was named after Halimede (Greek for "Sea Empress " ), one of about 50 sea nymphs Nereids in Greek mythology. They are the beautiful daughters of the wise old man Nereus, the prophecy and constant transformation have been rumored, and his wife, Doris of Oceanid.

Web properties

Halimede orbits Neptune in a retrograde, highly elliptical orbit 12261800-20917500 km Distance to the center ( large semi-major axis 16.5897 million or 669.911 Neptune radii ). The orbital eccentricity of 0.2608764. It is possible that the orbital parameters are variable, since the eccentricity with 0.5711, the orbital inclination ( with respect to the ecliptic ) with 134.101 ° and the Great semi-major axis from 15.728 to 16.611 Millionen km will be given. In this case Halimede Neptune would come even closer than the Apheldistanz of Nereid and cut their path. The orbit is inclined 99.06 ° relative to the equator of Neptune.

The orbit of the next inner moon Nereid is an average distance of about 11 million km from Halimedes orbit, the distance of the path of the next outer moon Sao averages about 5.6 million kilometers.

Halimede orbits Neptune in about 1,879 days 8 hours and 10 minutes or about 5,149 Earth years, ie longer than the four inner planets and the dwarf planet Ceres need around the sun.

Physical Properties

Halimede has a diameter of an estimated 62 km, based on the assumed for them albedo of 16%. The surface is thus relatively dark. Their density is estimated to be 1.5 g/cm3. So the moon is likely to be composed predominantly of water ice; the surface of Halimede appears gray in visible light.

Initially it was assumed that the moon is a captured asteroid. Since Halimede has a similar color to Nereid (which has, however, may be formed from the nebula in the Neptune system ), and since the probability of collision of the two bodies is given in the period of the existence of the solar system by 41 %, take many scientists that Halimede a could be abgesprengtes fragment of Nereid. Due to the large distance to Neptune and gravitational disturbances caused by the sun and other factors the moon could possibly get ( back ) into a heliocentric orbit.

Research

Because of the great distance to Neptune and weak brightness of 24.5 like the 1:4.760.000 is opposite to the central planet, Halimede was not found during the flyby of Voyager 2 in 1989. Since the discovery in 2002 Halimede could only be observed by ground-based telescopes, while their orbital elements and their brightness can be determined.

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