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3h ago

Interstellar Comet 3I/ATLAS Predates the Sun, VLT Study Finds

High-precision isotope measurements point to formation in a cold, metal-poor environment billions of years ago, signaling a need for larger telescopes to study fainter interstellar visitors.

This image of interstellar comet 3I/ATLAS was taken on 18 January 2026 with the FORS2 instrument on ESO’s Very Large Telescope (VLT). It is a stack of several images spanning 14 minutes. As the comet moves on the sky, the stars appear as trails in the background.
This image shows part of the spectrum of the interstellar comet 3I/ATLAS, captured in December 2025 with the UVES instrument on ESO’s Very Large Telescope. Image credit: ESO / C. Opitom / Manfroid et al. / O. Hainaut.

Overview

  • The Nature Astronomy paper published Monday reports VLT/UVES measurements showing unusually high ratios of carbon and nitrogen isotopes in 3I/ATLAS that differ from Solar System comets.
  • Independent JWST and other millimeter-wave observations corroborate the VLT data by detecting very high deuterium and elevated carbon fractions in the comet’s coma.
  • Researchers interpret these isotope patterns as evidence the comet condensed in a near-30 K, low-metallicity protoplanetary region that likely formed billions of years before the Sun.
  • Authors caution the age and birthplace estimates depend on chemical-evolution and condensation models and on reading coma gases rather than the buried nucleus, so some uncertainty remains.
  • The object is now receding and fading, and teams say next-generation facilities such as ESO’s ELT, Rubin Observatory surveys, and coordinated JWST/ALMA follow-ups will be needed to study fainter interstellar visitors and test whether 3I/ATLAS is typical.