The James Webb Space Telescope (JWST) has captured its first observation of the interstellar visitor 3I/ATLAS, producing results that astonished astronomers.
The powerful observatory turned its infrared gaze and Near-Infrared Spectrograph (NIRSpec) toward the comet on August 6, 2025.
Discovered on July 1 by the ATLAS survey telescope, 3I/ATLAS is only the third identified interstellar object entering our solar system. The others were 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.
JWST follows observations by the Hubble Space Telescope and SPHEREx Observatory, aiming to detail 3I/ATLAS’s size, physical properties, and chemical composition.
In a preprint paper, astronomers stressed that studying comets from other star systems helps reconstruct the conditions of their birth. These findings can be compared to knowledge of the solar system’s own formation 4.6 billion years ago.
As comets approach the sun, frozen materials sublimate directly into gases, creating the iconic coma and tail. Unsurprisingly, 3I/ATLAS displayed active outgassing.
JWST’s instruments detected carbon dioxide, water, water ice, carbon monoxide, and carbonyl sulfide in the comet’s coma.
Unexpectedly, the comet showed the highest carbon dioxide-to-water ratio ever measured in a comet. This may indicate that 3I/ATLAS’s core is inherently rich in carbon dioxide, perhaps exposed to stronger radiation than solar system comets.
Alternatively, this could suggest 3I/ATLAS formed within the “carbon dioxide ice line” of its original protoplanetary disk, where temperatures allowed CO₂ gas to freeze into solid ice.
The relatively low water vapor levels may also imply internal shielding that prevents solar heat from penetrating the comet’s icy nucleus. This would favor the release of carbon dioxide and carbon monoxide over water.
Earlier research even suggested that 3I/ATLAS may be around 7 billion years old, making it the oldest comet ever observed, nearly 3 billion years older than our solar system. Its steep trajectory indicates origins in the Milky Way’s thick disk, an ancient galactic region.
One certainty remains: the James Webb Space Telescope 3I/ATLAS study will continue until the comet exits the solar system, carrying away far fewer mysteries than it brought in.
