Webb spotted a subtle difference in the interstellar comets ice
NASA's James Webb Space Telescope finds interstellar comet 3I/ATLAS has very dusty ice, matching some freezing worlds beyond Neptune.
Astronomers have discovered a subtle difference in the ice of an interstellar comet, spotted by NASA's James Webb Space Telescope. The comet, 3I/ATLAS, was observed three times between August 2025 and April 2026 as it approached the sun. The telescope spread the comet's light into a rainbow, including infrared light invisible to human eyes.
Water ice absorbs light at specific points in the rainbow, making it possible to detect the ice, similar to a fingerprint. Most comets orbiting our sun display three marks in this pattern - a deep one and two faint ones. However, 3I/ATLAS showed only the deep mark and barely any of the faint ones. Researchers ran simulations and found that light scatters off comet grains in a similar way if tiny ice bits are mixed with more dust.
The dust blocks light from penetrating far into the ice, causing the faint marks to disappear. Though 3I/ATLAS initially appeared different from other icy comets in our solar system, it now seems to fit in among distant icy worlds in our own system. This suggests that ice may form in similar ways around different stars, with ice on various frozen worlds possibly having a consistent composition.
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