Interstellar Object 3I/ATLAS: Potentially the Oldest Comet Observed

An interstellar object, designated 3I/ATLAS, has emerged as a significant discovery in the field of astronomy, as researchers suggest it may be the oldest comet ever observed, potentially predating our solar system by over three billion years. This comet, rich in water ice, was first detected by the ATLAS survey telescope in Chile on July 1, 2025, when it was approximately 670 million kilometers from the Sun. Matthew Hopkins, an astronomer at the University of Oxford, revealed that the comet's age could be as much as seven billion years, making it a remarkable interstellar visitor, unlike previous objects observed in our solar system, such as 'Oumuamua and 2I/Borisov.

The discovery of 3I/ATLAS was presented by Dr. Hopkins during the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham. He explained that while most comets, such as Halley's Comet, originated within our solar system and are up to 4.5 billion years old, interstellar comets like 3I/ATLAS can provide insights into the early formation of celestial bodies. "All non-interstellar comets formed with our solar system, so are up to 4.5 billion years old," Hopkins stated. "But interstellar visitors have the potential to be far older, and of those known about so far, our statistical method suggests that 3I/ATLAS is very likely to be the oldest comet we have ever seen."

The trajectory of 3I/ATLAS indicates that it originated from the thick disk of the Milky Way, a region populated by ancient stars. According to Professor Chris Lintott, co-author of the study and presenter of the BBC's The Sky at Night, the comet has about a two-thirds probability of being older than the solar system. He emphasized the significance of this object, stating, "This is an object from a part of the galaxy we’ve never seen up close before. We think there’s a two-thirds chance this comet is older than the solar system, and that it’s been drifting through interstellar space ever since."

As 3I/ATLAS approaches the Sun, its surface will heat up, leading to cometary activity characterized by the outgassing of vapor and dust, which produces a glowing coma and tail. Early observations suggest the comet is already active and may surpass its interstellar predecessors in size. The implications of this discovery extend to future astronomical surveys, particularly with the upcoming Vera C. Rubin Observatory, which is expected to identify numerous interstellar objects. Dr. Rosemary Dorsey from the University of Helsinki noted, "The discovery of 3I suggests that prospects for Rubin may now be more optimistic; we may find about 50 objects, some similar in size to 3I."

The research conducted on 3I/ATLAS utilizes a model developed by Dr. Hopkins during his doctoral studies, which simulates the properties of interstellar objects based on their orbits and predicted stellar origins. This model, known as the Ōtautahi–Oxford Model, marks a pioneering application of predictive modeling to an interstellar comet. Dr. Michele Bannister from the University of Canterbury remarked on the excitement surrounding the comet’s activity, stating, "We’re in an exciting time: 3I is already showing signs of activity. The gases that may be seen in the future as 3I is heated by the Sun will test our model."

For amateur astronomers interested in observing 3I/ATLAS, it is expected to be visible through reasonably-sized telescopes in late 2025 and early 2026. This discovery not only sheds light on the origins of comets but also enhances our understanding of the processes involved in star and planet formation throughout the galaxy. As research continues, the implications of 3I/ATLAS could redefine our knowledge of interstellar objects and their role in the cosmos.