The interstellar comet 3I/ATLAS underwent notable chemical changes as it passed close to the Sun, offering new insights into the composition of objects formed beyond the solar system. Scientists say the findings could help refine understanding of how planetary systems develop.
The object, only the third known visitor from another star system, was observed using the Subaru Telescope by a team led by Yoshiharu Shinnaka. Researchers analyzed the comet’s surrounding gas cloud, known as the coma, and found that the ratio of carbon dioxide to water shifted after its closest approach to the Sun in October 2025, according to Space.com.
The coma forms when solar heat causes frozen material within a comet to sublimate, turning directly from solid to gas. By studying variations in the coma’s composition, scientists can infer details about the internal makeup of the comet’s nucleus.
In this case, the observed change suggests that the internal chemistry of 3I/ATLAS differs from its outer layers. As the comet approached the Sun, deeper materials were likely exposed, releasing gases with a different composition than those previously detected. This indicates a layered internal structure, shaped by its formation in a distant stellar environment.
The findings are significant because interstellar objects provide rare opportunities to study material formed outside the solar system. Unlike comets originating within it, these visitors carry chemical signatures from other regions of the galaxy, offering a direct comparison between different planetary formation environments.
Additional observations of 3I/ATLAS were also made by instruments aboard the JUICE mission, contributing to a broader dataset tracking the object’s behavior as it moved through the inner solar system.
Researchers say such studies will become increasingly important as new survey telescopes come online, improving the detection rate of interstellar objects. Each new discovery could expand the sample size available for analysis, helping scientists identify patterns in composition and evolution across different star systems.
The research team’s findings are scheduled for publication in The Astronomical Journal, with early versions already available through academic repositories.
