page_title: Nereid (moon)
section_title: Orbit and rotation
hierarchical_section_title: Nereid (moon) / Orbit and rotation
caption_attribution_description: English: The image shows Nereid's orbit.
context_page_description: Nereid, or Neptune II, is the third-largest moon of Neptune. Of all known moons in the Solar System, it has the most eccentric orbit. It was the second moon of Neptune to be discovered, by Gerard Kuiper in 1949.
context_section_description: 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. If the latter is true, it may be the only survivor of Neptune's original (pre-Triton capture) set of regular satellites.
  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, and other researchers for a time failed to detect any periodic modulation in Nereid's light curve from ground-based observations. In 2016, a clear rotation period of 11.594 ± 0.017 hours was determined based on observations with the Kepler space telescope.
caption: Nereid's highly eccentric orbit around Neptune.
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