Interstellar Object Search Awaits Third Visitor

Ancient Comet from Interstellar Space Offers Glimpse into Galaxy's Past

A mysterious object from interstellar space, newly found by astronomers, is being considered by scientists as the most ancient comet yet witnessed. Researchers associated with Oxford University suggest that the object, named 3I/Atlas, might have an age preceding the formation of the Sun's system by 3 billion years. An object coming from beyond our local solar neighborhood has been successfully identified on just two prior occasions. Initial results were unveiled in Durham during a national conference of the Royal Astronomical Society in the UK. The discovery has generated considerable excitement within the astronomical community.

A Landmark Discovery

The sighting of 3I/Atlas represents a significant moment for astronomy. The collective excitement about the discovery was voiced by Matthew Hopkins, an astronomer affiliated with Oxford University. He noted that his doctoral research involved four years of work forecasting the discovery of additional interstellar bodies, and this marks the first such find in his career. The object's velocity implies it possesses a remarkable age, possibly in excess of seven billion years. This could make 3I/Atlas the most extraordinary interstellar visitor documented to date, offering a unique sample of the ancient cosmos for study.

First Sighting in Chile

The initial sighting of 3I/Atlas was made on July 1, 2025, by the Atlas survey instrument located in Chile. When spotted, its separation from the Sun was approximately 670 million kilometres. At present, it remains a dim object that requires exceptionally powerful telescopes to be seen. Its distance from Earth is comparable to Jupiter's orbit. Since the initial observation, astronomers across the globe have been working intensely. Their work is centered on mapping its trajectory and learning additional information regarding its composition and background, a task that promises to reveal more about these celestial travellers.

An Interstellar Nomad

Interstellar objects are celestial bodies that are not gravitationally bound to a star and wander through space. They are essentially fragments of other planetary systems, ejected into the galactic void. Until recently, their existence was only theoretical. Scientists had long hypothesised that such objects roamed our galaxy, but they were expected to be exceedingly rare. The detection of the first two visitors, 1I/ʻOumuamua and 2I/Borisov, and now 3I/Atlas, has reshaped this understanding. It suggests that these interlopers are far more common than previously imagined.

The Trail of 'Oumuamua

The first confirmed interstellar visitor, 1I/ʻOumuamua, was discovered in October 2017 by the Pan-STARRS1 telescope in Hawaii. Its name, a Hawaiian word for "messenger from afar arriving first," reflects its groundbreaking status. The object had a distinctly hyperbolic path, which meant its journey through the solar system was a one-time event. Unlike a typical comet, ʻOumuamua showed no signs of releasing dust or gas, leading to much debate about its classification. Its unusual, elongated shape, estimated to be up to 240 metres long but only 40 metres wide, further deepened the mystery surrounding its origin and composition.

A More Familiar Visitor: 2I/Borisov

Two years after ʻOumuamua's fleeting visit, a second interstellar object was found. In August 2019, amateur astronomer Gennadiy Borisov, using a self-built telescope in Crimea, discovered 2I/Borisov. This object behaved much more like a conventional comet. It displayed a visible coma and tail, formed as solar heating vaporised its icy surface. This allowed astronomers to study its chemical makeup in greater detail. Borisov offered a useful contrast to the puzzling ʻOumuamua, demonstrating that visitors from other stars can bear a resemblance to the comets originating in our star system.

A Suspected Ancient Origin

A theory from Matthew Hopkins points to an origin for 3I/Atlas within the Milky Way's "thick disk." This region contains a scattered collection of very old stars, whose orbits take them over and under the galactic plane where our star is situated. If the object did form around one of these old stars, it would be composed of primordial materials from a much earlier cosmic era. An overhead depiction of the galactic structure provides a visual for its likely trajectory, which is rendered in red, while the Sun's path appears in yellow. This origin story makes 3I/Atlas a direct link to the galaxy's distant past.

A Comet's Fiery Tail

The research team theorises that 3I/Atlas has a composition rich in water ice, a consequence of its probable formation around an ancient star. When this cosmic traveller gets nearer to our star in the coming months, it is set to experience a significant change. Increasing solar radiation is going to warm the body's exterior, which will make the ice sublimate. This action will expel large clouds of gas and particles out into the void. This process might lead to the formation of a brilliant, glowing tail, a signature feature of a classic comet, creating a spectacular sight for observers.

Modelling the Visitor

The researchers' conclusions about the nature and origin for 3I/Atlas stem from a sophisticated model. This predictive tool was developed by Matthew Hopkins himself. The model simulates the properties of interstellar objects based on their observed orbits and likely stellar points of origin. Professor Chris Lintott, who contributed to the study as a co-author, remarked on the unique chance this object presents. He explained that its origins are in a region of space we have not previously had the chance to observe in detail, offering a rare sample of a different galactic neighbourhood.

Image Credit - BBC

A Window into the Past

Professor Lintott further elaborated on the profound significance of the object. The group's calculations suggest a two-in-three likelihood that the comet's age exceeds that of the sun's system. They think it has been moving through the emptiness of deep space from the moment it formed. This makes it a relic of a bygone cosmic era. As Hopkins detailed, bodies from interstellar space take shape near other stars during the initial existence of those stars. This clear connection to the original stars gives researchers a way to examine the varied star groups throughout our galaxy.

How Objects Escape Their Home

Planetary systems are dynamic environments where gravitational interactions constantly sculpt the orbits of celestial bodies. One primary way objects become interstellar nomads is through ejection from their home systems. A close encounter with a giant planet can act like a gravitational slingshot, accelerating a smaller body, like a comet or asteroid, to a speed great enough to escape its star's pull. This process is believed to have happened in our own early star system. Planetary migration, such as Neptune's outward journey, likely scattered countless smaller objects into interstellar space.

The Role of Binary Stars

Binary star systems, where two stars orbit a common centre of mass, are particularly effective at ejecting objects. Studies suggest that these systems are far more likely to produce interstellar objects than single-star systems like our own. The complex and powerful gravitational forces within a binary system can easily fling wandering planetesimals into the galactic wilderness. It is estimated that for rocky objects similar to ʻOumuamua, more than 95 per cent likely originate from binary systems. This provides a crucial clue for tracing the origins of these cosmic messengers.

The Chemistry of a Traveller

Analysis of 2I/Borisov revealed a composition that was both familiar and strange. While many of its chemical signatures resembled those of comets from our star system, it had a surprisingly high concentration of carbon monoxide. This suggests that it formed in an extremely cold environment, possibly around a red dwarf star, which is smaller and cooler than our Sun. The high carbon monoxide level could indicate that 2I/Borisov was a fragment of a small planet, rich in this volatile ice, which was shattered by a collision.

Awaiting a Celestial Display

As 3I/Atlas continues its journey through our local system, it is predicted to become more visible. In the coming months, viewing the object should become possible for people on Earth who use non-professional telescopes. This offers a thrilling opportunity for skywatchers and citizen scientists to witness a visitor from another star system. Its approach toward the solar body will likely increase its brightness and activity, potentially making it one of the most observed interstellar objects to date. Astronomers are eagerly anticipating the chance to gather more data as it becomes more prominent in the night sky.

A New Era of Discovery

Globally, astronomers are preparing for a fresh era of sky-watching centered on the Vera C. Rubin Observatory in Chile. The powerful new instrument will commence a complete scan of the sky in the southern hemisphere in the coming months. Researchers anticipate that its decade-long survey will uncover anywhere from five to fifty more interstellar visitors. This will transform the field from the study of isolated events into the analysis of a whole population of celestial visitors.

The Power of the Rubin Observatory

The Vera C. Rubin Observatory is an technological marvel. Perched atop Cerro Pachón, it benefits from the clear, dark skies of the Chilean Andes. The observatory features an 8.4-metre telescope paired with the largest digital camera ever constructed. This combination will allow it to scan the entire visible southern sky every few nights, creating an unprecedented time-lapse movie of the universe. Its primary mission, the Legacy Survey of Space and Time (LSST), will revolutionise our understanding of transient phenomena, from exploding stars to wandering interstellar comets.

Finding Faint Visitors

The key to discovering additional interstellar bodies lies in detecting extremely faint bodies at vast distances. The Rubin Observatory is perfectly suited for this task. Its wide field of view and large aperture give it a unique advantage in spotting these elusive targets. By spotting these bodies sooner as they approach, while they are distant from the solar body and extremely faint, the facility allows for a longer period of follow-up study by other telescopes. This capability will be crucial for characterising these visitors before they speed away back into deep space.

Interstellar Archaeology

Every interstellar body that journeys through our star system acts as a time capsule from a different galactic region. They are the building blocks of exoplanets, carrying clues about the composition and evolution of their home systems. By studying a large sample of these objects, astronomers can start to assemble a picture of the varied planetary arrangements that exist throughout our galaxy. This method gives researchers the ability to study the leftover materials from planet creation around faraway stars, all from within our star system.

The Challenge of the Chase

Studying these objects is a race against time. Interstellar visitors travel at incredible speeds, often giving scientists less than a year to organise observation campaigns. Planning missions to intercept them is an even greater challenge. A spacecraft would need to be launched with extreme speed to catch up to a fast-moving object. Concepts like placing interceptor spacecraft in a ready "storage orbit" are being explored. Another futuristic proposal involves using powerful lasers to push a spacecraft equipped with a solar sail, enabling it to accelerate rapidly for a rendezvous.

The Future of Interstellar Science

The discoveries of ʻOumuamua, Borisov, and now the prospective 3I/Atlas have opened a new frontier in astronomy. The anticipated flood of new discoveries from the Rubin Observatory promises to revolutionise our understanding of planet formation and galactic evolution. What were once theoretical curiosities are now tangible objects of study. These envoys from other star systems offer a direct method for analyzing the wide-ranging and complex chemistry found across the Milky Way. The coming decade holds the promise of a catalogue of interstellar objects, each with a story to tell about its stellar home.