Comet From Another Star System Is Overflowing With Rubbing Alcohol

Keypoints:

• Interstellar comet 3I/ATLAS shows exceptionally high methanol levels compared to solar system comets
• ALMA measured methanol-to-hydrogen cyanide ratios of 70 and 120, among the highest ever recorded
• The research was led by Nathan Roth of American University
• Icy grains around the comet release methanol like miniature comets of their own
• Findings were published September 9

Astronomers pointed ALMA's Atacama Compact Array at 3I/ATLAS, only the third confirmed interstellar object ever detected, and found it carrying an unusually large amount of methanol, the same molecule found in rubbing alcohol. 

"Observing 3I/ATLAS is like taking a fingerprint from another solar system," said lead author Nathan Roth, a professor at American University. "It's bursting with methanol in a way we just don't usually see in comets in our own solar system."

The team tracked two molecules in the comet's glowing coma: methanol and hydrogen cyanide, a nitrogen-based compound common in most comets. On two separate observing dates, methanol outnumbered hydrogen cyanide by ratios of 70 to 1 and 120 to 1, placing 3I/ATLAS among the most methanol-rich comets ever studied, far beyond typical levels in our own solar system.

The two molecules didn't even come from the same place. Hydrogen cyanide escaped mostly from the comet's solid core, the pattern seen in ordinary solar system comets. Methanol came from both the core and from tiny icy grains scattered through the coma, grains that behaved like miniature comets of their own, releasing gas as sunlight warmed them. That kind of detailed outgassing behavior has never been traced this precisely in an object from outside our solar system before.

The chemistry points to a different origin story entirely. A comet this methanol-rich likely formed under conditions unlike anything that shaped the comets orbiting our own sun, evidence that other star systems can build their icy building blocks in genuinely different ways.