Comet 3I/ATLAS Spewed Methane As It Passed the Sun, Revealing Hidden Ices Beneath Its Surface
Comet 3I/ATLAS will soon leave our solar system for good, but new clues about its identity continue to be revealed as it gradually disappears from view. Ongoing research has reconstructed the unconventional composition of 3I/ATLAS, and now another ingredient emanating from the interstellar visitor has been discovered: methane.
A new study published in Letters from the astrophysical journal confirmed that 3I/ATLAS emitted more and more methane as the sun passed by. As the comet warmed, volatile ices on its surface began to turn directly into gas, revealing what 3I/ATLAS is made of. Although they have limited time to examine 3I/ATLAS, researchers believe their observations could shed light on the comet’s strange origins.
“This is a very interesting object,” lead author Matthew Belyakov, a graduate student at the California Institute of Technology, said in a statement. “It has been traveling across the galaxy for at least a billion years. The high speed at which it flew past us only gave us a narrow window to study it.”
Learn more: New images of comet 3I/ATLAS reveal ‘how magical the universe could be’
Detection of methane in comet 3I/ATLAS
Comet 3I/ATLAS captivated the world in late 2025 when it flew past the Sun and Earth, becoming the third interstellar object to visit the solar system. As the sun approached, astronomers observed a bright blue aura developing around the comet; This display, called a coma, is typical of comets that move near the sun.
The coma of 3I/ATLAS indicated that the ices on its surface were sublimating (transforming from a solid to a gas under the effect of the heat of the sun).
The researchers jumped at the chance to observe this reaction, looking for different types of ice to get an idea of the elements and compounds contained in 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 seen by humans) from 3I/ATLAS.
By examining these signatures, the researchers discovered that 3I/ATLAS began emitting more methane as it was warmed by the sun. This methane came specifically from the internal layers; The researchers believe that the outer layers may have experienced a significant heating period while the comet was still in its original planetary system, before being 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. The heat from the sun then reached the icy inner layers of the comet; This allowed researchers to get a good look at what was inside 3I/ATLAS, not just what was on its surface.
Clues on the composition
Other observations outside of the new study have compiled details about 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 core, according to NASA.
In November 2025, just after the comet made its closest approach to the sun, the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) space probe observed it spewing 4,409 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 from oxygen, hydrogen and carbon atoms present in the gas and dust around 3I/ATLAS, showing that these elements extended up to 3.1 million kilometers from the core.
One last chance to observe 3I/ATLAS
Although 3I/ATLAS exhibits many typical comet behaviors, a few features 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 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 to study the comet in hopes of understanding where it might have come from.
“JWST will look at 3I/ATLAS once again this spring,” Belyakov said. “It’s already becoming difficult to observe; it’s now near Jupiter.”
Learn more: Radio signals detected by comet 3I/ATLAS: what its interstellar origins reveal
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