Nereid (moon)
Voyager 2 image (1989)
|
|
| Discovery | |
|---|---|
| Discovered by | Gerard P. Kuiper |
| Discovery date | 1 May 1949 |
| Designations | |
| Pronunciation | /ˈnɪəri.ɪd/ or /ˈnɛri.ɪd/ |
| Adjectives | Nereidian, Nereidean |
| Orbital characteristics | |
| Epoch J2000 | |
| Periapsis | 1372000 km (0.00917 AU) |
| Apoapsis | 9655000 km (0.06454 AU) |
| 5513787 km (0.03685 AU) | |
| Eccentricity | 0.7507 |
| 360.1362 d | |
|
Average orbital speed
|
934 m/s |
| Inclination |
|
| Satellite of | Neptune |
| Physical characteristics | |
|
Mean radius
|
170±25 km |
| 0.48 d (11 h, 31 min) | |
| Albedo | 0.155 |
| Temperature | ≈ 50 K mean (estimate) |
Nereid is the third-largest moon of Neptune. It has a highly eccentric orbit. It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949.
Nereid was discovered on 1 May 1949 by Gerard P. Kuiper on photographic plates taken with the 82-inch telescope at the McDonald Observatory. He proposed the name in the report of his discovery. It is named after the Nereids, sea-nymphs of Greek mythology and attendants of the god Neptune. It was the second and last moon of Neptune to be discovered before the arrival of Voyager 2 (not counting a single observation of an occultation by Larissa in 1981).
Nereid orbits Neptune in the prograde direction at an average distance of 5,513,400 km (3,425,900 mi), but its high eccentricity of 0.7507 takes it as close as 1,372,000 km (853,000 mi) and as far as 9,655,000 km (5,999,000 mi).
The unusual orbit suggests that it may be either a captured asteroid or Kuiper belt object, or that it was an inner moon in the past and was perturbed during the capture of Neptune's largest moon Triton.
In 1991, a rotation period of Nereid of about 13.6 hours was determined by an analysis of its light curve. In 2003, another rotation period of about 11.52 ± 0.14 hours was measured. However, this determination was later disputed. Other researchers have so far failed to detect any periodic modulation in Nereid's light curve.
Nereid is Neptune's third-largest satellite and has an average radius of about 170 kilometres (110 mi). It is rather large for an irregular satellite. The shape of Nereid is unknown.
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