340 km
ESTIMATED DIAMETER
360.13 DAYS
ORBITAL PERIOD
5.51 million km
AVERAGE DISTANCE FROM NEPTUNE
1949
DISCOVERED
HIGH
ORBITAL ECCENTRICITY
#2
DISTANT MAJOR MOON
THE ECCENTRIC MOON
Nereid is one of Neptune's outer moons
and one of the most unusual objects in
the Neptune system.
It was discovered in 1949 by astronomer
Gerard Kuiper and was the second moon
of Neptune to be discovered.
Nereid has an extremely eccentric orbit.
Its distance from Neptune changes
dramatically during each revolution,
taking it from relatively close to the
planet to millions of kilometres away.
Because of its unusual orbit and irregular
shape, Nereid is thought to have a very
different history from Neptune's regular
inner moons.
Voyager 2 photographed Nereid during
its 1989 encounter with Neptune.
NEREID FEATURES
EXTREME ORBIT
Nereid has one of the most eccentric
orbits of any known natural satellite
in the Solar System.
DISTANT WORLD
At its most distant point, Nereid
travels millions of kilometres away
from Neptune.
VOYAGER 2
Voyager 2 photographed Nereid
during its historic flyby of the
Neptune system in 1989.
DID YOU KNOW?
Nereid's orbit is so eccentric that
its distance from Neptune changes
by millions of kilometres
during one orbit.
AN EXTREMELY ECCENTRIC ORBIT
Nereid follows a highly eccentric orbit around Neptune, carrying it through a very large range of distances from the planet. This unusual orbit distinguishes it from Neptune's compact inner moons.
One hypothesis is that the capture of Triton strongly disrupted Neptune's original satellite system, potentially altering orbits or ejecting earlier moons. Nereid's present orbit is therefore studied as a clue to that violent dynamical history.
IMAGE:
NASA / JPL / VOYAGER 2
NEREID IMAGE VIA WIKIMEDIA COMMONS
NEREID IMAGE VIA WIKIMEDIA COMMONS