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Story summary
- Astronomers using the Subaru Telescope on Mauna Kea observed comet 3I/ATLAS on Jan. 7, 2026 and found its carbon-dioxide-to-water ratio had dropped.
- ALMA measured a deuterium-to-hydrogen ratio above 6 × 10?³—over 40 times Earth’s ocean value—indicating the comet formed in a very cold environment below about 30 K.
- Yoshiharu Shinnaka of the Koyama Space Science Institute said lower ratio suggests solar heating exposed interior layers, findings that were reported in The Astronomical Journal on April 22, 2026.
