The mysterious interstellar object 3I/ATLAS fascinated scientists as it made its way through the inner solar system last year, closely passing by several planets before careening back into space, never to be seen again.

Researchers continue to pore over the treasure trove of data ground- and space-based telescopes gathered about the object, which affords an extremely rare up-close glimpse at an object from beyond our star system.

Most recently, scientists analyzed new data collected by the Mid-Infrared Instrument (MIRI) attached to NASA’s James Webb Space Telescope — and made a curious discovery. In the words of the European Space Agency, the telescope “sniffed methane” from the mysterious lump of ice, dust, and rock in mid- and late-December, roughly two months after its perihelion, or when it made its closest approach of the Sun.

In other words, 3I/ATLAS appears to have let one rip as it whipped through our cosmic neighborhood.

Flatus jokes aside, the significance of the first-ever chemical fingerprint of an interstellar object can’t be understated. For one, it’s the first time we’ve ever detected methane gas while observing an interstellar object, hinting at a highly intriguing origin story that differs from familiar comets in our own solar system.

The MIRI images, as detailed in a new paper published in the journal The Astrophysical Journal Letters, show the distribution not just of methane, but of carbon dioxide and water as well.

Since the gas was released after perihelion, a period when comets give off the most amount of material as they’re heated up, scientists suggest the methane was buried deep below the comet’s surface before it emerged from beneath a thick, icy shell. That’s especially true likely since methane is extremely volatile and sublimates from ice into gas very easily, as NASA points out.

Furthermore, the amount of methane scientists found relative to water in the object was surprisingly high when compared to other solar system comets. The latest observations also corroborate previous findings that 3I/ATLAS was abundant in carbon dioxide, making it stand out even more.

“Both these findings point to a very different formation environment and chemistry than the vast majority of comets that formed within our Solar System,” the ESA wrote.

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