Ancient Comet 3I/ATLAS Unveils Secrets of Early Galaxy

Astronomers have identified an ancient interstellar object named 3I/ATLAS, which could potentially be the oldest comet ever observed, dating back over seven billion years. Discovered by a research team from the University of Oxford, this ice-rich comet is believed to have originated from a region far beyond our solar system, providing new insights into how comets form and evolve.

The significance of 3I/ATLAS lies in its remarkable age, suggesting it predates the formation of the Sun and planets. Unlike typical comets that formed within our solar system, 3I/ATLAS is thought to have emerged from the Milky Way’s thick disk, an area populated with ancient stars. The object’s composition and trajectory may offer valuable information about the early galaxy and the interstellar processes that influenced star and planetary development.

3I/ATLAS: A Rare Visitor from Interstellar Space

The detection of 3I/ATLAS marks only the third instance of an object entering our solar system from interstellar space, following the visits of 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019. Dr. Matthew Hopkins, an astronomer at the University of Oxford, explained that its orbit indicates it came from the thick disk of the galaxy, a region that lies above and below the flat plane where the Sun resides.

At the Royal Astronomical Society’s National Astronomy Meeting 2025, Hopkins highlighted the uniqueness of this finding, stating, “All comets within our solar system, such as Halley’s, formed about 4.5 billion years ago. But interstellar comets like 3I/ATLAS may have formed long before that, potentially making this the oldest comet ever observed.”

Discovery and Characteristics of 3I/ATLAS

3I/ATLAS was first detected on July 1, 2025, by the ATLAS survey telescope located in Chile. At that time, it was approximately 670 million kilometers from the Sun, travelling on a steep and unusual orbit that immediately attracted the attention of astronomers.

Utilizing a statistical model developed during his doctoral research, Hopkins and his team predicted the age and composition of interstellar comets based on their orbits and potential stellar origins. Their analysis indicated that 3I/ATLAS likely formed near an ancient star in the thick disk, implying a high concentration of water ice.

Professor Chris Lintott, co-author of the study and presenter of BBC’s The Sky at Night, remarked, “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, releasing gas and dust from its icy surface, which will create a bright coma and tail typical of comets. Early observations are already indicating signs of such activity, suggesting that 3I/ATLAS could be larger and more dynamic than its predecessors, ʻOumuamua and Borisov.

Dr. Michele Bannister from the University of Canterbury in New Zealand noted, “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 sets it apart from other known comets. Formed around ancient stars, it may carry chemical signatures from the early Milky Way, preserving crucial information about the conditions that existed long before the Sun’s formation. Analyzing its composition could yield insights into how interstellar comets contribute to star and planet formation throughout the galaxy.

Future Prospects and Significance

The discovery comes at a pivotal time as Hopkins and his colleagues prepare for survey operations with the Vera C. Rubin Observatory, which is expected 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.”

The Rubin telescope’s wide-field imaging capabilities will allow astronomers to observe interstellar objects in greater detail than ever before, potentially reshaping our understanding of comet origins and their role in distributing organic materials across galaxies.

In a personal reflection, Hopkins shared the excitement of the discovery, which coincided with the defense of his doctoral thesis focused on modeling interstellar comet populations. “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 research team has published their findings as a preprint on arXiv, introducing the Ōtautahi–Oxford Model, the first predictive framework effectively applied to a newly discovered interstellar comet.

For astronomy enthusiasts looking to witness this historic event, 3I/ATLAS is expected to become visible through medium-sized amateur telescopes by late 2025 or early 2026, depending on its brightness and activity. As it travels through our solar system, scientists hope to uncover more about the ancient origins of comets, the evolution of galaxies, and the interstellar chemistry that may one day illuminate the beginnings of life in the universe.