Orbit and Rotation
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) from the planet.
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 the moon's light curve. Later in 2003 another rotation period of about 11.52 ± 0.14 hours was measured. However this determination was later disputed. Other researchers have failed so far to detect any periodic modulation in Nereid's light curve.
Read more about this topic: Nereid (moon)
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