Nereid (moon)
Gerard P. Kuiper
Nereid or Nereid ( Neptune II) is the third- largest moon of the planet Neptune. He has one of the most eccentric orbits a planet moon in the solar system.
Discovery and designation
Nereid was discovered on May 1, 1949 by Gerard Kuiper Peter. She was the second known moon of Neptune was discovered because of the dark surface and about eight times smaller in diameter compared to the only known and by far the largest of Neptune moon Triton until 103 years after that. The discovery was made on photographic plates, which were made with the 82 -inch telescope of the McDonald Observatory. Kuiper suggested the name Nereid before in his discovery report.
It was named after the moon about 50 Nereids, sea nymphs of 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
Orbit
Nereid orbits Neptune on a prograde, highly elliptical orbit 1353600-9623700 km Distance to the center ( large semi-major axis 5.5134 million kilometers or 222.653 Neptune radii ). The orbital eccentricity is 0.7507; this is the most eccentric orbit of a known moon in the solar system (which might, however, from 2004 discovered Saturn's moon Bestla is exceeded ). No irregular outer moon of the gas giant planets of the outer solar system is so close to its parent planet. The orbit is inclined 32.55 ° relative to the equator of Neptune.
The orbit of the next inner moon Triton is an average distance of 5.159 million km Nereids orbit, due to the high orbital eccentricity comes Nereid Triton to about 1 near one million kilometers. The removal of the next outer moon Halimede averages about 10 million km.
The irregular path could be an indication that Nereid was originally an object of the Kuiper belt, which was captured by the gravitational force of Neptune. Another explanation would be that Nereids unusual train is due to gravitational disturbances of Neptune's largest moon Triton.
Nereid orbits Neptune in approximately 360 days 3 hours 16 minutes and 7 seconds, which is a scarce Earth year.
Rotation
Nereid rotates in about 11 hours and 31 minutes ( 11.52 ± 00:14 hours) around its own axis.
Physical Properties
Nereid has an average diameter of 340 km and is the third largest moon of Neptune. It is also the largest of the irregular satellites in the solar system. The moon appears elongated on the recordings of the Voyager 2 probe, it is therefore not spherical.
In the spectrum of Nereid appear gray. Spectral Nereid be moved between the Uranian moons Titania and Umbriel, suggesting a surface composition of water ice - which was identified by the group of Michael E. Brown 1998 - and indicates spectrally neutral material. From the spectrum ago Nereid is more akin to Proteus as Triton and is strikingly different than the asteroids in the outer solar system, such as the centaur Pholus, Chiron or Chariklo, which rather suggests an origin in the Neptune system as a captured asteroid.
The total area is about 360,000 km2 and is thus roughly the size of Germany. The average surface temperature of -223 ° C ( ~ 50 K) estimated.
The next outer moon Halimede may be a fragment of Nereid, which is caused by a collision.
Research
Before the Neptune flyby of the Voyager 2 spacecraft in the summer of 1989 Nereid could only be observed by ground-based telescopes, while their orbital elements and their brightness can be determined.
Since the Voyager 2 flyby based on the priority of a nearby Triton Passage Naherkundung not been possible Nereid between 20 April and 19 August 1989, happened in a minimum distance of 4.65288 million kilometers on August 24. It could be made 83 pictures in resolutions 43-800 km. Although hardly surface details could be made out from the pictures, could be determined about the size and color as well as the higher compared to the other small moons Neptune albedo.
Since the flyby of the Neptune system ground-based observations as well as the Hubble Space Telescope has been studied intensively.