Nereid as a Regular Satellite of Neptune
arXiv:2606.02818 · doi:10.1126/sciadv.aeb1429
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.
This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science Advances on May 20, 2026