Comet 3I/ATLAS ‘spewed methane as it passed the Sun’ – but has no fossils?

Credit: NSF/AUI/NSF NRAO/M.Weiss

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This looks like yet another nail in the coffin of the ‘methane gas is a fossil fuel’ assertion, to add to the methane cycle and lakes on Saturn’s moon Titan, for example. No mention of rotting vegetation or dinosaur remains here. Perhaps it could be argued that the comet somehow broke off from an Earth-like planet or moon somewhere? Or perhaps not.
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Comet 3I/ATLAS will soon leave our Solar System for good, but new clues on its identity are still being revealed as it gradually fades from sight, says Discover magazine.

Ongoing research has pieced together the unconventional composition of 3I/ATLAS, and now, yet another ingredient has been found emanating from the interstellar visitor: methane.

A new study published in The Astrophysical Journal Letters has confirmed that 3I/ATLAS increasingly emitted methane upon passing the sun.

As the comet warmed up, volatile ices on its surface began to directly turn into gas, unveiling what 3I/ATLAS is made of. Despite having a limited amount of time to examine 3I/ATLAS, researchers believe their observations could illuminate the comet’s outlandish origins.
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Detecting Methane In Comet 3I/ATLAS
Comet 3I/ATLAS captivated the world in late 2025 when it flew past the sun and Earth, being only the third interstellar object to visit the Solar System. As it approached the sun, astronomers observed a bright blue aura developing around the comet; this display, called a coma, is typical of comets that travel near the sun.

The coma of 3I/ATLAS indicated that the ices on its surface were sublimating (transforming from a solid into a gas due to the sun’s heat).

Researchers jumped at the opportunity to observe this reaction, looking for different types of ices to get an idea of the elements and compounds within 3I/ATLAS. The new study, for example, used advanced instruments on NASA’s James Webb Space Telescope to examine mid-infrared signatures (wavelengths of light 10 times longer than those humans see) coming from 3I/ATLAS.

By examining these signatures, researchers found that 3I/ATLAS began to emit more methane as it was warmed by the sun.

This methane was specifically coming from the inner layers; the researchers believe that the outer layers may have experienced a significant period of heating while the comet was still in its original planetary system, before it was ejected into the cold interstellar medium.
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A Final Chance to Observe 3I/ATLAS
While 3I/ATLAS displayed many typical comet behaviors, there are a few characteristics that set it apart.

According to the Lowell Observatory, the comet unexpectedly showed much higher levels of carbon dioxide than water vapor on its way to the sun, and the dust particles around it appeared to reflect light in a way that hinted at an unusual structure.

Although time is running out to observe 3I/ATLAS, researchers will continue investigating the comet with the hope of understanding where it may have come from.

Full article here.
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Image: Comet 3I/ATLAS [credit: NSF/AUI/NSF NRAO/M.Weiss]