JWST finds dusty water ice in interstellar comet 3I/ATLAS

The James Webb Space Telescope detected water ice in interstellar comet 3I/ATLAS as submicron grains mixed with dust, producing a spectrum that matches Kuiper Belt objects rather than typical solar system comets. NIRSpec observed the comet at 3.3 AU on August 6, 2025, at 2.4 AU on December 22, 2025, and at 5.7 AU on April 1, 2026.

• Strong 3.0-micron ice band, with 1.5- and 2.0-micron bands weak or absent
• 3I/ATLAS spectrum resembles Kuiper Belt icy worlds, not ordinary comets
• Comet discovered July 1, 2025, traveling up to ~222,500 km/h
• Post-perihelion data hint at crystalline ice near 3.1 microns