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JWST Data Point to Cosmic-Ray–Altered Crust on Interstellar Comet 3I/ATLAS

New analysis finds the outgassing now seen likely samples only an irradiated outer layer tens of meters deep.

Overview

  • JWST/NIRSpec and SPHEREx measured CO2/H2O about 7.6 and CO/H2O about 1.65, with an unusually red spectrum that departs from solar system comet trends.
  • Researchers attribute these signatures to long-term galactic cosmic ray processing, supported by lab work showing CO is converted to CO2 and an organic-rich crust forms.
  • Modeling indicates present activity releases material from a processed shell roughly 15–20 meters deep rather than from pristine interior ice.
  • Perihelion occurred on Oct. 29, and coordinated follow-ups with JWST, SPHEREx, Keck and NASA’s Swift are tracking post-perihelion changes that could, though unlikely, expose fresher material.
  • Separate reports citing a JPL fit raise claims of “non-gravitational acceleration” and color changes near perihelion, but these remain unverified and could reflect conventional outgassing behavior.