Interstellar Comet 3I/ATLAS Unveils Hidden Chemistry Near the Sun

New measurements of interstellar comet 3I/ATLAS show its coma chemistry changing after a close pass to the Sun, with the CO2-to-water ratio shifting between observations in late 2025 and early 2026 (including Subaru data from Jan 7, 2026 and JUICE observations in Nov 2025). The results imply the comet’s internal chemistry differs from its external makeup, offering insights into planetesimal and planet formation in other star systems; the work by Yoshiharu Shinnaka and collaborators will be published in the Astronomical Journal on April 22, 2026.