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Title: Do interstellar comets differ in composition from Solar System comets?
Plain: 2I/Borisov carried an unusually large share of carbon monoxide and 3I/ATLAS showed a coma dominated by carbon dioxide. Whether such differences reflect where they formed or billions of years of cosmic-ray exposure in space is unknown.
Precise: Compare volatile and metal abundance ratios ($\mathrm{CO}/\mathrm{H2O}, \mathrm{CO2}/\mathrm{H2O}, \mathrm{Ni}/\mathrm{Fe}$) of 2I/Borisov and 3I/ATLAS with Solar System comets, and determine whether the differences reflect formation location and stellar environment or processing during Gyr-long interstellar travel. The answer is a classification of composition differences by origin, with predictions testable on future objects.
Settled by: Spectroscopic surveys of a sample of interstellar comets compared with laboratory and model predictions of cosmic-ray processing of ices.
Kind: well-posed
Answer type: classification
References: (empty)
Literature status: open
Status note: JWST spectra in 2025 showed a CO2-dominated coma of 3I/ATLAS ($\mathrm{CO2}/\mathrm{H2O} \sim 8$), VLT spectra detected nickel vapor with little or no iron, and its non-gravitational acceleration near perihelion is attributed to outgassing.
Posed since: (empty)