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4h ago

New Study Finds Interstellar Comet 3I/ATLAS Has a Cosmic-Ray–Altered, CO2-Rich Crust

Post-perihelion observations focus on whether erosion exposes pristine material beneath an estimated 15–20 meter irradiated layer.

an image of a comet streaking through space with the stars around it reflecting rainbows
Image of comet 3I/ATLAS captured by the Gemini Multi-Object Spectrograph on Gemini South at Cerro Pachón in Chile (Credit : International Gemini Observatory/NOIRLab/NSF/AURA)
Image
Researchers used NASA's James Webb Space Telescope to observe 3I/ATLAS on Aug.

Overview

  • JWST/NIRSpec and SPHEREx measured extreme coma ratios for 3I/ATLAS, with CO2/H2O at 7.6±0.3 and CO/H2O at 1.65±0.09, alongside markedly red spectral slopes.
  • The latest arXiv synthesis attributes the composition to long-term galactic cosmic-ray processing that converts CO to CO2 and builds an organic-rich crust consistent with the observed spectra.
  • Modeling and erosion estimates indicate current outgassing samples only a GCR-processed shell roughly 15–20 meters deep rather than the comet’s pristine interior.
  • The object reached perihelion on Oct. 29, and separate analyses report an unusually rapid pre-perihelion brightening detected by SOHO, STEREO, and GOES-19 that remains unexplained.
  • Media coverage highlights claims of non-gravitational acceleration and color changes based on cited JPL data, which are unconfirmed and secondary to the compositional results.