Halimede (moon)
| Halimede | |
|---|---|
| Provisional or systematic name | S / 2002 N 1 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | 16,589,670 km |
| Periapsis | 12,261,810 km |
| Apoapsis | 20,917,520 km |
| eccentricity | 0.2608764 |
| Orbit inclination to the equator of the central body | 99.06 ° |
| Orbit inclination to the ecliptic | 111.87514 ° |
| Orbital time | 1879.34 d |
| Mean orbital velocity | 0.56 km / s |
| Physical Properties | |
| Albedo | ≈ 0.16 |
| Apparent brightness | 24.5 mag |
| Medium diameter | ≈ 62 km |
| Dimensions | ≈ 8.9920 · 10 16 kg |
| Medium density | ≈ 1.5 g / cm 3 |
| Acceleration of gravity on the surface | ≈ 0.0065 m / s 2 |
| Escape speed | ≈ 19.85 m / s |
| discovery | |
| Explorer |
Matthew J. Holman et al. |
| Date of discovery | August 14, 2002 |
| Remarks | Possibly a blown fragment of Nereid |
Halimede (also Neptune IX ) is the tenth innermost and innermost of the outer retrograde irregular moons of the planet Neptune . It may have been caused by a collision of Neptune's third largest moon, Nereid, with another body.
Discovery and naming
Halimede was founded on August 14, 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 discovered on recordings from August 14th to September 4th 2002 and August 10th 2001 together 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 images were digitally combined until the moons, in contrast to the line-shaped stars, appeared point-like. The discovery was announced on January 13, 2003; the moon was initially given the provisional designation S / 2002 N 1 .
On February 3, 2007, the moon was named after Halimede (Greek for “ruler of the sea”), one of the 50 or so Nereids from Greek mythology .
Track properties
Halimede orbits Neptune on a retrograde , very elliptical orbit between 12,261,800 and 20,917,500 km from its center (major orbit half-axis 16,589,700 or 669,911 Neptune radii). The orbital eccentricity is 0.2608764. It is possible that the orbit parameters are variable, since the eccentricity is also given as 0.5711, the orbit inclination (compared to the ecliptic ) with 134.101 ° and the major orbit half-axis between 15.728 and 16.611 million km. In this case, Halimede would come even closer to Neptune than the apheld distance of Nereid and its orbit intersect. The orbit is 99.06 ° inclined to the equator of Neptune.
The orbit of the next inner moon Nereid is on average about 11 million km from Halimedes orbit, the distance of the orbit of the next outer moon Sao is on average about 5.6 million km.
Halimede orbits Neptune in around 1,879 days, 8 hours and 10 minutes or around 5,149 earth years, i.e. longer than the four inner planets and the dwarf planet Ceres need around the sun.
Physical Properties
Halimede is estimated to be 62 km in diameter based on the assumed retroreflective power of 16%. The surface is therefore relatively dark. Their density is estimated at 1.5 g / cm 3 . The moon is therefore likely to be composed predominantly of water ice ; Halimede's surface appears gray in visible light.
Initially, the moon was believed to be a captured asteroid. Since Halimede has a similar color to Nereid (which may have formed from the primordial nebula in the Neptune system), and since the probability of collision between the two bodies in the period of the existence of the solar system is given as 41%, many scientists assume that Halimede is a could be a blown off fragment of Nereid. Due to the great distance to Neptune and gravitational disturbances from the sun and other factors, the moon could possibly also enter a heliocentric orbit (again).
exploration
Due to the great distance to Neptune and the weak brightness of 24.5 mag, which is 1: 4,760,000 compared to the central planet, Halimede was not found during the flyby of Voyager 2 in 1989. Since its discovery in 2002, Halimede could only be observed through earth-based telescopes and their orbital elements and their brightness could be determined.
Web links
- IAUC 8047: Satellites of Neptune Jan 13, 2003 (discovery)
- IAUC 8193: Satellites of Neptune September 3, 2003 (rediscovery)
- IAUC 8802: Satellites of Neptune February 3, 2007 (numbering and naming)
- IAU: Natural Satellites Ephemeris Service IAU: Orbital parameters and ephemeris of irregular moons
- NASA: Planetary Satellite Physical Parameters NASA: Physical Parameters (English)
- NASA: Planetary Satellite Mean Orbital Parameters NASA: Orbital Parameters (English)
- NASA: Neptunian Satellite Fact Sheet NASA: List of Parameters
- Scott S. Sheppard: Neptune's Known Satellites List with parameters of the Neptune system (English)
- USGS: Planet and Satellite Names and Discoverers Names of planets and satellites
- German moon page: The outer moons of Neptune images from Halimede
- Polish moon page: Halimede description and further links (English)