Interstellar comet 3I/ATLAS shows record-high methanol levels, outgassing from icy grains
Observations with ALMA reveal that interstellar comet 3I/ATLAS contains unusually large amounts of methanol, far exceeding typical solar-system comets.
ALMA observations of interstellar comet 3I/ATLAS captured a striking chemical fingerprint, with methanol abundances that dwarf those of almost all comets from our own solar system. Measurements on two dates gave methanol-to-hydrogen cyanide ratios of roughly 70 and 120, marking the object as exceptionally methanol-rich. The data indicate that methanol originates from both the comet’s nucleus and from minute icy grains suspended in the surrounding coma, which act like miniature comets as they sublimate.
This dual-source outgassing contrasts with the typical HCN-only release seen in solar-system comets. The results imply that the ice in 3I/ATLAS formed under, or was later altered by, conditions unlike those that shaped most local cometary material. As only the third confirmed interstellar visitor, 3I/ATLAS provides a rare glimpse into the chemistry of distant planetary systems.
Why it matters
The comet’s unique chemistry offers new clues about how icy bodies form around other stars.
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