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yesterday

ALMA Finds Interstellar Comet 3I/ATLAS Strikingly Methanol‑Rich With Unusual Outgassing

Preprint analyses using ALMA with JWST indicate a cold, ancient origin as the fading visitor nears a brief pass by Jupiter.

3I/ATLAS likely originated somewhere within the Milky Way's thick disk (red lines) before crossing paths with our sun along its orbit around the galaxy (yellow lines).
Image
Image
3I/ATLAS

Overview

  • ALMA spectra from late 2025 measured methanol‑to‑hydrogen cyanide ratios of roughly 70 and 120, placing 3I/ATLAS among the most methanol‑rich comets studied.
  • Imaging shows hydrogen cyanide largely venting from the nucleus while methanol also releases from detached icy grains in the coma, a pattern consistent with hyperactive behavior.
  • JWST observations from Dec. 22, 2025 report isotope ratios, including elevated deuterium in water and atypical carbon ratios, that suggest formation in very cold conditions near 30 kelvins.
  • The JWST team’s age inference of about 10–12 billion years and the ALMA chemistry results are described in preprints and institutional summaries and remain under peer review.
  • Now outbound as only the third confirmed interstellar object, 3I/ATLAS is fading with a closest approach to Jupiter expected on March 15, narrowing the window for follow‑up measurements.