In 2016, extended observations with the Kepler space telescope showed only low-amplitude variations (0.033 magnitudes). Nereid's rotation could be either in the state of forced precession or even chaotic rotation (like Hyperion) due to its highly elliptical orbit.
To date there is no credible explanation of the variations, but, if they exist, they are likely related to the rotation of Nereid. This means that they may be quite chaotic. On the other hand, not all astronomers who have observed Nereid have noticed such variations. They persist even after a correction for distance and phase effects.
Since 1987 some photometric observations of Nereid have detected large (by ~1 of magnitude) variations of its brightness, which can happen over years and months, but sometimes even over a few days. Nereid is similar in size to Saturn's moon Mimas, though Nereid is denser. It is rather large for an irregular satellite. Nereid is third-largest of Neptune's satellites, and has a mean radius of about 180 kilometres (110 mi). 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). It is named after the Nereids, sea-nymphs of Greek mythology and attendants of the god Neptune.
He proposed the name in the report of his discovery. Kuiper on photographic plates taken with the 82-inch telescope at the McDonald Observatory. It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949. It has the most eccentric orbit of all known moons in the Solar System. Nereid, or Neptune II, is the third-largest moon of Neptune.
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