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arXiv · 2606.02818

Nereid as a Regular Satellite of Neptune

Matthew Belyakov·M. Ryleigh Davis·Ian Wong·Konstantin Batygin·Michael E. Brown
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Abstract

Nereid, Neptune's third largest moon, is considered to be a captured irregular satellite due to its highly eccentric orbit. However, among irregular satellites, Nereid is an outlier: it is the largest, the closest to its host planet, and the most eccentric. We present James Webb Space Telescope near-infrared spectroscopy of Nereid that demonstrates that its composition is inconsistent with its suggested captured origin. We then simulate Nereid's early orbital history subsequent to Triton's capture to demonstrate a plausible dynamical pathway for a regular satellite formed in-situ around Neptune to evolve to Nereid's present-day orbit. Based upon the available spectroscopic and dynamical evidence, we propose that Nereid is not a body captured from the Kuiper belt, but rather the sole surviving intact regular satellite of Neptune.

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Matthew Belyakov, M. Ryleigh Davis, Ian Wong, Konstantin Batygin, Michael E. Brown. 2026-06-01. Nereid as a Regular Satellite of Neptune. https://doi.org/10.1126/sciadv.aeb1429

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