Nereid is a small moon orbiting Neptune, and was discovered in 1949 by reknowned Dutch astronomer Gerard Peter Kuiper.

Nereid is approximately 340 kilometers (210 miles) in diameter. Its orbit is so far from Neptune that it requires 360 days to make it around.

Nereid's orbit is the most eccentric of any moon in the solar system. Its distance to Neptune ranges from about 1,353,600 kilometers (841,100 miles) to 9,623,700 kilometers (5,980,200 miles).

Nereid is Neptune's most distant moon and was named for the mythical sea nymphs that were the daughters of Nereus and Doris. Neptune's other seven moons are Triton, Naiad, Thalassa, Despina, Galatea, Larissa, and Proteus.

We know very little about this moon, but what we do know is rather interesting. Nereid has the most eccentric orbit of any moon that we have ever discovered. Its orbital path is so extreme that it varies in distance from Neptune by as much as 5,000,000 miles over the course of its 360 day orbit. This extremely elliptical orbit has caused some researchers to speculate that Nereid was originally a Kuiper Belt object, or asteroid that was captured by Neptune's gravity in the recent past (recent, as in the last few million years).

This moon was first discovered by noted astronomer Gerard Peter Kuiper in 1949. We have only been able to gather minimal data about this moon since then. The Voyager probe has been the main source of what little knowledge we do have, but even it only passed within 3,000,000 miles. But that was close enough to snap a few pictures, and gather some information on the size and possible makeup of this satellite. The Voyager photos showed that Nereid reflects 14 percent of the light that strikes it (even more than our moon), but that data really hasn't told us much, and we are still just guessing at the mass and composition of this satellite.

  • Equatorial radius 170 km
  • Equatorial radius (Earth = 1) 2.6654e-02
  • Mean distance from Neptune 5,513,400 km
  • Orbital period 360.1362 days
  • Mean orbital velocity 1.12 km/sec
  • Orbital eccentricity 0.7512
  • Orbital inclination 27.6 degrees
  • Visual geometric albedo 0.14
  • Magnitude 18.7

Ne"re*id (?), n.; pl. E. Nereids (#), L. Nereides (#). [L. Nereis, -idis, gr. , , a daughter of Nereus, a nymph of the sea, fr. Nereus, an ancient sea god; akin to wet, Skr. nara water, cf. Gr. to flow.]

1. Class. Myth.

A sea nymph, one of the daughters of Nereus, who were attendants upon Neptune, and were represented as riding on sea horses, sometimes with the human form entire, and sometimes with the tail of a fish.

2. Zool.

Any species of Nereis. The word is sometimes used for similar annelids of other families.


© Webster 1913.

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