Subaru Telescope Reveals New Data on the Interior Composition of 3I/ATLAS

The Subaru Telescope observed the interstellar comet 3I/ATLAS (C/2025 N1) on January 7, 2026 (UT), after it made its closest approach to the Sun. By observing colors in the coma around the comet, astronomers could estimate the ratio of carbon dioxide to water. This ratio is much lower than that inferred from earlier observations by space telescopes. These findings suggest that the chemistry of the coma is evolving over time and offers clues to the structure of comet 3I/ATLAS.