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3h ago

Ancient, Cold Origin Found for Interstellar Comet 3I/ATLAS

High-precision isotope spectra point to formation in a very cold, metal-poor environment with a model-dependent age up to about 12 billion years.

Comet in the Solar System. Image Credit: Banana Nano.
The Hubble Space Telescope image of the interstellar comet 3I/ATLAS on July 21, 2025, when the comet was 277 million miles from Earth in this handout image obtained by Reuters on June 22, 2026. Hubble shows that the comet has a teardrop-shaped cocoon of dust coming off its solid, icy nucleus. NASA, ESA, David Jewitt (UCLA); image Processing: Joseph DePasquale (STScI)/Handout via REUTERS
NASA dismissed the suggestion that the comet could be an alien spacecraft
Scientists the comet could the oldest -- and maybe coldest object ever observed in our Solar System

Overview

  • A Nature paper published Monday reports JWST NIRSpec observations, backed by ALMA and VLT data, showing extreme isotopic ratios in 3I/ATLAS that differ from any Solar System body.
  • The comet’s water is highly enriched in deuterium at D/H ≈ 0.98%, more than an order of magnitude above known Solar System comets, which implies water formed at temperatures below about 30 K.
  • Measured 12C/13C ratios in CO and CO2 exceed typical Solar System values, and when read through Galactic chemical-evolution models they can imply accretion as long as ~10–12 billion years ago.
  • Spectra show a natural cometary mix of CO2, carbon-bearing molecules and water ice, which largely rules out earlier speculation of an artificial origin, while authors note alternative natural scenarios and model uncertainties.
  • 3I/ATLAS was first seen by ATLAS in July 2025, passed perihelion in October 2025, is now outbound near 8 AU, and will leave the heliosphere decades from now as future surveys aim to find more interstellar visitors.