JWST Detects Methane on Interstellar Comet 3I/ATLAS for First Time at 2.54 AU
Updated
Updated · Space.com · Jun 5
JWST Detects Methane on Interstellar Comet 3I/ATLAS for First Time at 2.54 AU
3 articles · Updated · Space.com · Jun 5
Summary
Methane was detected spewing from 3I/ATLAS in JWST observations taken after the comet’s Oct. 29, 2025 perihelion, marking the first confirmed methane seen on any interstellar object.
Dec. 27 repeat observations at 2.54 AU proved crucial: water vapor had dropped sharply after the comet crossed the solar system’s snow line, while methane and carbon dioxide remained active because they vaporize more easily.
JWST also confirmed abundant carbon dioxide and nickel vapor, and the team said carbon monoxide outgassing surged to 40 times carbon dioxide in December, reinforcing how unusual 3I/ATLAS is versus solar-system comets.
Researchers think the methane appeared late because it was buried deep in the nucleus, with surface methane likely stripped away by earlier heating in its home planetary system before ejection into interstellar space.
The methane-to-water and carbon-dioxide-to-water ratios suggest 3I/ATLAS formed in a chemically different environment—possibly 11 billion to 12 billion years ago—offering a rare probe of planet formation beyond the solar system.
Does this interstellar comet's strange chemical mix hint at different recipes for life-bearing planets?
What secrets of its alien star system does this ancient comet's strange chemistry hold?
First Detection of Methane on Interstellar Object 3I/ATLAS: Webb Telescope Unveils Unprecedented Chemistry and Cold Formation Environment
Overview
In December 2025, the James Webb Space Telescope made a historic discovery by detecting methane on the interstellar comet 3I/ATLAS, marking the first time this key organic molecule was found on an object from outside our solar system. Using the advanced Mid-Infrared Instrument (MIRI), scientists obtained detailed spectra from the region around the comet, allowing them to identify and map gases like methane. As only the third known interstellar visitor, 3I/ATLAS offers a rare glimpse into the chemistry of distant star systems, helping researchers understand how planets and comets form in environments very different from our own.