JWST finds clay minerals on Neptune's inner moons, hinting at shattered ancient satellites

Using the James Webb Space Telescope, scientists led by former Caltech graduate student Ryleigh Davis examined Neptune's rings and three inner moons—Larissa, Galatea and Proteus. Spectra of Larissa, Galatea and the rings displayed magnesium-rich phyllosilicates, minerals that require liquid water to form, yet no water-ice was detected on these bodies. The team argues the clays must have come from the interiors of much larger icy moons that were shattered when Neptune captured its massive moon Triton, destroying the planet's original satellite system.

Proteus lacked the clay signature, possibly indicating it formed from a different portion of the debris or was later heated. An independent JWST study by Matthew Belyakov supports the idea that Nereid may be the only intact remnant of that early system. The findings offer a rare glimpse into the deep interiors of ancient icy worlds, now exposed by a violent planetary event.