NASA's James Webb Space Telescope has detected methane on 3I/ATLAS, the third interstellar object ever observed passing through our solar system. The finding adds to a growing chemical portrait of a comet that researchers believe may predate the Sun by billions of years.
A Visitor From Another Star
3I/ATLAS was discovered on July 1, 2025, by the ATLAS survey. Its steeply hyperbolic orbit, with an extreme eccentricity and a velocity that marks it as gravitationally unbound to the Sun, confirms that it originated around another star before drifting into our neighborhood.
Estimates suggest the object may have formed 10 to 12 billion years ago, which would make it older than the solar system itself and one of the most ancient comets ever studied. If that age holds, the comet would carry frozen material assembled in the early galaxy, long before our Sun and planets came together.
Interstellar objects are rare prizes for astronomers because they let scientists examine matter forged around other stars without sending a spacecraft across the vast distances between systems. Only two such visitors had been confirmed before this one, making every observation of 3I/ATLAS valuable.
What Webb Found
- Methane signature: Webb's June 2026 observations identified methane in the comet's gas output, a molecule of strong interest for understanding the chemistry of distant planetary systems.
- Carbon dioxide richness: Earlier Webb data showed 3I/ATLAS releasing unusually large amounts of carbon dioxide relative to water compared with typical solar-system comets.
- Red, featureless spectrum: Optical observations revealed a red coma, with colors resembling some distant trans-Neptunian objects.
An Object Studied Across the Spectrum
3I/ATLAS has become one of the most intensively observed interstellar objects on record. Between January 15 and 22, 2026, NASA's TESS mission conducted dedicated time-series observations. Late in 2025, the X-ray telescopes XRISM and XMM-Newton detected a diffuse X-ray glow around the comet's nucleus, making it the first interstellar comet observed in X-ray light.
Separately, SETI scientists searched the object for radio signals that might indicate technology of non-natural origin. They reported finding nothing beyond human-made interference, consistent with 3I/ATLAS being a natural comet.
Why It Matters
Each interstellar object offers a rare sample of material assembled around a distant star. By measuring the gases 3I/ATLAS releases as it warms near the Sun, scientists can compare its chemistry with comets formed in our own system. The high carbon-dioxide output and now the methane detection suggest its ices froze under conditions different from those that shaped familiar comets.
As the comet continues its journey back toward interstellar space, observation windows are closing. Researchers are working to gather as much data as possible while the visitor remains within reach of telescopes, knowing it will not return.
The intensive campaign around 3I/ATLAS also serves as a rehearsal for the future. Survey telescopes coming online are expected to detect many more interstellar objects in the years ahead, and the techniques refined on this comet, from infrared spectroscopy to X-ray imaging, will help astronomers respond quickly when the next one appears.