For more than a billion years, a chunk of frozen ice the size of a small mountain drifted through the dark space between stars. Then, in the summer of 2025, it crossed into our solar system, swung around the Sun, and started heading back out into the void. As it left, it exhaled something no human had ever measured on an object like it before: methane.
On June 1, 2026, NASA announced that its James Webb Space Telescope had made the first-ever direct detection of methane on an interstellar object. The object is comet 3I/ATLAS, the third known visitor to pass through our solar system from another star, first spotted in July 2025.
What makes this discovery so strange is not just the methane itself, but how much of it there is. Compared with comets born in our own solar system, 3I/ATLAS is releasing a surprising amount of methane relative to water. It is also unusually rich in carbon dioxide. To scientists, these numbers tell a clear story: this comet did not form here. It came together in a very different region, around a very different star, under conditions our own neighborhood never experienced.
Interstellar comets are valuable because they are leftover material from the formation of planets around distant stars. Their ices are direct physical samples of chemistry we could otherwise never touch. NASA used Webb's Mid-Infrared Instrument to study the comet when it was about 205 million miles from the Sun in December 2025. As the comet moved farther away and cooled, the gases began to fade. Water dropped off the fastest, because it is less volatile than methane or carbon dioxide. This sequence helped researchers understand how the comet was layered.
The work was led by Caltech graduate student Matthew Belyakov, with Ian Wong of the Space Telescope Science Institute as co-first author. Their results were published in The Astrophysical Journal Letters. For anyone worried, NASA was clear: the comet poses no threat to Earth. It is already past Jupiter's orbit and will not return.