Study finds Neptune moon Nereid likely formed with Neptune, not Kuiper Belt

A new study suggests Neptune's moon Nereid is likely the sole survivor of the planet's original family of satellites, having endured the chaotic arrival of the system's largest moon, Triton, billions of years ago. The findings, published in the journal Science Advances, challenge the long-held theory that Nereid itself was captured from the distant Kuiper Belt.

Researchers led by the California Institute of Technology used NASA's James Webb Space Telescope to analyze Nereid's composition. They found its properties, including a high abundance of water ice and a lack of certain volatile organics, are inconsistent with known Kuiper Belt objects. This indicates Nereid probably formed alongside Neptune rather than being an interloper snared by the planet's gravity.

Neptune's largest moon, Triton, is widely believed to have been captured from the Kuiper Belt, a vast region of icy bodies beyond Neptune's orbit. That ancient gravitational capture is thought to have violently disrupted the planet's original satellite system, scattering or destroying other moons. Scientists say Nereid's survival was likely due to its ejection into an extreme, elliptical orbit around Neptune, a trajectory...