Astronomers have identified an ancient interstellar object named 3I/ATLAS, which may be older than the solar system itself, possibly dating back over seven billion years. Discovered by a research team from the University of Oxford, this ice-rich comet provides a rare opportunity to examine the early processes in our galaxy.
The origins of 3I/ATLAS are traced to the thick disk of the Milky Way, a region abundant with ancient stars. Its unique composition and trajectory could reveal significant insights into the formation of stars and planetary systems. This discovery is particularly exciting as it marks only the third occasion that astronomers have recognized an object entering our solar system from interstellar space, following the notable visits of 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019.
According to Dr. Matthew Hopkins, an astronomer at the University of Oxford, the comet”s orbit suggests it originated from the galaxy”s thick disk, which is located above and below the flat plane where the Sun and most stars are found. During a presentation at the Royal Astronomical Society”s National Astronomy Meeting 2025 in Durham, Hopkins stated, “All comets within our solar system, such as Halley”s, formed about 4.5 billion years ago. However, interstellar comets like 3I/ATLAS may have formed long before that, potentially making this the oldest comet ever observed.”
The object was first spotted on July 1, 2025, by the ATLAS survey telescope located in Chile, when it was approximately 670 million kilometers from the Sun. Its steep and unusual orbit immediately drew the attention of astronomers. The research team utilized a statistical model developed by Hopkins during his doctoral studies to predict the age and composition of interstellar comets based on their orbits and probable stellar origins. Their findings indicated that 3I/ATLAS likely formed around an ancient star from the thick disk, suggesting a high concentration of water ice within the comet.
Co-author of the study, Professor Chris Lintott, noted, “This is an object from a part of the galaxy we”ve never seen up close before. There”s a two-thirds chance this comet is older than the solar system itself, a true relic from our galaxy”s distant past.”
As 3I/ATLAS approaches the Sun, scientists expect it to exhibit increased activity. The rising temperatures will cause sublimation, leading to the release of gas and dust from its icy surface, thus forming a bright coma and tail typical of comets. Initial observations have already indicated signs of such activity, suggesting that 3I/ATLAS may be larger and more dynamic than its interstellar predecessors. This makes it an important subject for future astronomical missions.
Dr. Michele Bannister from the University of Canterbury in New Zealand remarked, “We”re entering an exciting phase. As 3I warms up under the Sun”s light, we”ll be able to study the gases it releases, providing a rare glimpse into material formed in another part of the Milky Way.”
The potential age of 3I/ATLAS distinguishes it from other comets. Formed around ancient stars, it may hold chemical signatures from the early Milky Way, preserving vital information about the conditions that existed long before the Sun”s formation. Analyzing its composition could enhance our understanding of how interstellar comets contribute to the formation of stars and planets in the galaxy.
Additionally, the trajectory of 3I/ATLAS reveals that it dives deep into the outer thick disk, a region that is seldom studied through astronomical observations. In contrast, the Sun orbits much closer to the galactic plane, underscoring the remarkable nature of material from such a distant area reaching our vicinity.
The timing of 3I/ATLAS”s discovery is particularly promising, as Hopkins and his team were preparing for survey operations with the Vera C. Rubin Observatory, which is anticipated to revolutionize our understanding of transient cosmic objects. Dr. Rosemary Dorsey from the University of Helsinki explained, “The Rubin Observatory is projected to detect between five and fifty interstellar objects in the coming years. But the discovery of 3I suggests we may find even more, perhaps dozens of these ancient wanderers.”
Ironically, just a week after defending his doctoral thesis focused on modeling interstellar comet populations, Hopkins was met with a flurry of messages confirming the discovery of 3I/ATLAS. “Rather than a calm Wednesday, I woke up to messages saying “3I!!!!!!!!!!”,” he recalled. “It”s thrilling to test our theoretical model on a brand-new, possibly ancient object in real time.” The team has published their analysis as a preprint on arXiv, introducing the Ōtautahi–Oxford Model, the first predictive framework successfully applied to a newly discovered interstellar comet.
Astronomy enthusiasts will have the opportunity to view 3I/ATLAS through medium-sized telescopes by late 2025 and early 2026, depending on its brightness and activity. As it continues its journey through the solar system, scientists hope it will yield further insights into the ancient origins of comets and the evolution of galaxies, as well as the interstellar chemistry that may eventually explain the emergence of life in the universe.
