Webb Observations Reveal Unusual Ice-Grain Pattern in Interstellar Comet 3I/ATLAS

The James Webb Space Telescope observed 3I/ATLAS with its NIRSpec instrument on three occasions spanning August 2025 to April 2026, before and after the comet’s closest approach to the Sun. The reported spectra showed a strong absorption feature near 3 microns, while features near 1.5 and 2 microns appeared weak or absent.

Key details

• Researchers modeled the spectrum as evidence that the comet released water-ice grains smaller than a micron, mixed with substantial dust.
• The reported ice spectrum resembles that of some carbon-dioxide-rich trans-Neptunian objects, which orbit beyond Neptune.
• A separate 2025 JWST study reported a carbon-dioxide abundance among the highest observed in a comet.
• The study was reported as published in The Astrophysical Journal Letters on October 26, 2026.

The reported spectrum showed strong absorption near 3 microns, with weak or absent features near 1.5 and 2 microns.

Why it matters

The spectrum gives researchers a way to compare the icy material in an interstellar comet with distant icy bodies in our solar system. The researchers interpret the resemblance as a possible link to trans-Neptunian-object-like material, while the observations do not establish where 3I/ATLAS formed.