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2d ago

Webb and SPHEREx Confirm CO2-Dominated Coma Around Interstellar Comet 3I/ATLAS

The latest spectra highlight an extreme carbon-to-water ratio that points to unusual formation conditions, with a nucleus far fainter than its surrounding coma.

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NASA’s SPHEREx space observatory was photographed at BAE Systems in Boulder, Colorado, in November 2024 after completing environmental testing. The spacecraft’s three concentric cones help direct heat and light away from the telescope and other components, keeping them cool.
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Overview

  • JWST NIRSpec data from August 6 reveal a carbon dioxide–dominated coma with detections of H2O, CO, OCS, water ice and dust, plus enhanced outgassing toward the Sun.
  • The measured CO2/H2O mixing ratio is about 8±1, among the highest recorded in any comet and well above trends seen in Solar System comets.
  • NASA’s SPHEREx observations from August 7–15 independently map a bright, extended CO2 coma, reinforcing a carbon‑rich composition.
  • Analyses indicate that more than 99% of the observed brightness arises from the coma, leading teams to revise the nucleus size down to roughly a few kilometers.
  • A coordinated campaign with Webb, Hubble, SPHEREx, Rubin and ground observatories continues ahead of late‑October perihelion and a safe December pass, with no evidence supporting an artificial origin.