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. 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.
“It’s a very interesting object,” said lead author Matthew Belyakov, a graduate student at the California Institute of Technology, in a statement. “It has been traveling through the galaxy for at least a billion years. The high speed at which it flew past us gave just a narrow window to study it.”
Read More: New Images of Comet 3I/ATLAS Reveal “How Magical the Universe Could Be”
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.
As a result, the volatile ices on the outer shell of 3I/ATLAS may have already been somewhat depleted before entering our Solar System. Warmth from the sun, then, reached the comet’s icy inner layers; this allowed the researchers to get a good look at what was inside of 3I/ATLAS, not just what was on its surface.
Clues on Composition
Other observations outside of the new study have compiled details on the composition of 3I/ATLAS. In August 2025, NASA’s SPHEREx space observatory detected an abundance of carbon dioxide in its coma and water ice in its nucleus, according to NASA.
In November 2025, right after the comet made its closest approach to the sun, the European Space Agency’s JUICE (Jupiter Icy Moons Explorer) spacecraft observed it spewing out 4409 pounds of water vapor every second, the equivalent of 70 Olympic swimming pools per day, according to the ESA.
JUICE’s Ultraviolet Imaging Spectrograph also captured light coming from oxygen, hydrogen, and carbon atoms in the gas and dust around 3I/ATLAS, showing that these elements stretched as far back as 3.1 million miles from the nucleus.
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.
“JWST is going to look at 3I/ATLAS one more time this spring,” Belyakov said. “It’s already getting tough to observe; it’s now out by Jupiter.”
Read More: Radio Signals Detected From Comet 3I/ATLAS — What Its Interstellar Origins Reveal
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