Overview
- A Caltech-led paper published May 20 used a 10-minute James Webb infrared spectrum to show Nereid’s surface is unusually water-rich with some CO2, a composition that does not match the Webb-measured sample of Kuiper Belt objects.
- The study’s numerical simulations of Triton’s capture found that when Triton survives its chaotic arrival about one quarter of runs leave one or more original moons on distant, eccentric orbits similar to Nereid’s.
- Nereid is large for an irregular satellite at roughly 210–220 miles (338–350 km) across and orbits Neptune on a highly elongated path that takes about an Earth year to complete.
- Outside scientists described the result as plausible and important but provisional, and the authors say more Webb observations or a dedicated spacecraft flyby would be needed to confirm Nereid’s native origin; no Neptune mission is currently planned.
- The finding fits a long-standing idea that Triton’s retrograde capture billions of years ago scattered or destroyed Neptune’s original moons and that the small inner moons now seen are likely rubble from that violent reshaping of the system.