Accepted Interstellar-Comet Study
3I/ATLAS carries a volatile recipe unlike the usual Solar System comet
VLT spectra across perihelion reveal severe ammonia-related depletion and unusual carbon-chain chemistry in material formed around another star.
Briefed September 23, 2026 · Aliens in the Clouds
Measured Spectra · Composition Interpreted
Researchers used the UVES spectrograph on ESO's Very Large Telescope to follow interstellar comet 3I/ATLAS from August 2025 before perihelion through February 2026 after perihelion. The high-resolution near-ultraviolet and optical spectra measured emissions from OH, NH, CN, C3, CH, and C2, allowing the team to compare gas-production rates and abundance ratios on both sides of the comet's closest approach to the Sun.
The accepted study finds NH and NH2 strongly depleted, indicating a severe shortage of ammonia-related volatiles, alongside carbon-chain depletion and abundance relationships outside the canonical Solar System comet cluster. Some observed ratios evolve with heliocentric distance, which the authors attribute to coma processes such as hyperactivity rather than changes inside the nucleus. The result expands the known chemistry of comets formed around other stars; it does not identify an artificial composition or technological origin.
Why it matters
A chemically distinctive interstellar comet gives planetary scientists a direct sample of how volatile reservoirs in another system can differ from those that built our own comets.
What the source establishes
Accepted observational research using repeated calibrated spectra. Molecular emissions and production trends are measured; nucleus composition and the physical causes of some abundance patterns remain inferred.
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