James Webb telescope reveals comet 3I/ATLAS for the first time: not a spacecraft, but interesting behavior

The James Webb Space Telescope (JWST) has observed for the first time the mysterious comet 3I/ATLAS, which briefly flew into the solar system.

JWST observed 3I/ATLAS with infrared cameras and a near-infrared spectrograph on August 6 this year. The 3I/ATLAS object was discovered on July 1, 2025 with the ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope. 

This is only the third interstellar object to be discovered got into the solar system. Two other interstellar aliens were the asteroid 1I/’Oumuamua, discovered in 2017, and comet 2I/Borisov, discovered in 2019. 

Prior to James Webb, Comet 3I/ATLAS had already been observed by the Habble and “SPHEREx”. The goal of the observations is to determine the characteristics of 3I/ATLAS, including size, physical properties, and chemical composition. In the initial publication, the astronomers, who observed 3I/ATLAS with JWST noted, that the study of similar comets from other star systems helps to understand the conditions that existed in these systems during their formation. These results are comparable to what scientists have learned about the conditions in the solar system 4.6 billion years ago, when planets, asteroids, and comets were forming. 

As the comet approaches the Sun, it heats up, and the frozen substances in the comet’s composition change from a solid to a gaseous state. This is what forms the comet’s characteristic tail and halo — or “coma“. The astronomers used JWST and its spectrograph to detect carbon dioxide, water, water ice, carbon monoxide, and carbonyl sulfide in the 3I/ATLAS coma. 

The most unexpected was the largest ratio of carbon dioxide to water ever observed in a comet. This may tell scientists, what conditions were used to form Comet 3I/ATLAS. 

In particular, the high content of the presence of carbon dioxide in this comet may indicate, that 3I/ATLAS is rich in carbon dioxide inside. This may mean, that the comet contains ices, that have been exposed to much stronger radiation, than comets in the solar system.

Another alternative version, which the researchers do not rule out, suggests, that the high carbon dioxide content in the 3I/ATLAS may indicate, that this comet may have formed in a specific location, called “carbon dioxide ice line”, inside the swirling cloud of matter or protoplanetary disk, that surrounded the parent star. This is defined as the point at which the temperature around the young star, or “protostar,” drops low enough for carbon dioxide to change from a gaseous state to a solid.

At the same time, scientists also note, that the low water vapor content may indicate the presence of 3I/ATLAS, something that prevents heat from penetrating the ice core. This can prevent water from converting from ice to gas compared to the rate of conversion of carbon dioxide and carbon monoxide.

The results of previous observations have shown, that the age of the comet 3I/ATLAS may be about 7 billion years old. Thus, it may become the oldest comet ever observed. It may be older than the solar system by about 3 billion years. 

A group of researchers, who conducted previous studies of the comet, came to this conclusion after studying the steep trajectory of Comet 3I/ATLAS through the Solar System. This suggests, that the comet originates from the “thick disk” of the Milky Way, which consists of stars, — a region of our Galaxy much older than the “thin disk” in which the Sun was born.

The preprint with the results of the study is published on Zenodo.org

Source: Space.com