Neptune's Inner Moons and Rings Are Exposed Icy Body Interiors

Abstract

Neptune's single large moon, Triton, is accompanied by a set of dusty rings and small moons whose composition and origin are uncertain. Using the James Webb Space Telescope, we observed Neptune's rings and three moons: Larissa, Galatea, and Proteus. Remarkably, these moons and rings have spectra that are distinct from other outer solar system objects and show no evidence of water ice, despite hosting deep 3 micron OH absorption bands. Additionally, Larissa, Galatea, and the rings show a compositional signature unique among outer solar system bodies: a 2.72 micron absorption band diagnostic of magnesium-rich phyllosilicates - a signpost of extensive aqueous alteration. These minerals likely formed in the interior of primordial satellites destroyed during Triton's violent capture or a tidally shredded dwarf planet. Our findings suggest that Neptune's present-day inner moons and rings reaccreted from this deep interior material and therefore uniquely access the interior composition of icy outer solar system differentiated bodies.

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 July 29, 2026

References in corpus (12)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Formation of Regular Satellites from Ancient Massive Rings in the Solar System
• Did Saturn's rings form during the Late Heavy Bombardment ?
• Ring Formation around Giant Planets by Tidal Disruption of a Single Passing Large Kuiper Belt Object
• 3-micron Reflectance Spectroscopy of Carbonaceous Chondrites under Asteroid-like Conditions
• JWST near-infrared spectroscopy of the Lucy Jupiter Trojan flyby targets: Evidence for OH absorption, aliphatic organics, and CO${}_2$
• Compositions and origins of outer planet systems: Insights from the Roche critical density
• Triton's Evolution with a Primordial Neptunian Satellite System
• The origin of Neptune's unusual satellites from a planetary encounter
• JWST Spectrophotometry of the Small Satellites of Uranus and Neptune
• Spectral trends across the rings and inner moons of Uranus and Neptune from JWST NIRCam images
• Nereid as a Regular Satellite of Neptune