The Remarkable Discovery of Interstellar Objects
Less than a decade ago, the idea of detecting an object from another solar system within our own was largely regarded as science fiction . Astronomers were aware of their existence but believed that the chances of detecting such objects were practically negligible . This perception changed in 2017, a year that marked a significant turning point in the study of interstellar bodies.
1i/’Oumuamua: The First Interstellar Visitor
The first object to change our understanding of interstellar bodies was 1i/’Oumuamua . When it appeared, it baffled astronomers for numerous reasons, the primary one being that it was the first interstellar object ever discovered in our solar system. Its shape was peculiar—some described it as cigar-shaped , while others likened it to a flat pancake . Measuring approximately 100 to 200 meters in length, it passed by our Sun, leaving behind a trail of questions: Was it a comet, an asteroid, or something entirely new? The debate continues even as ‘Oumuamua moves further away from us.
2i/Borisov: The Second Interstellar Object
Just as we were pondering whether we would ever witness another interstellar object, the answer came unexpectedly. In 2019 , astronomers discovered the second object from another star system, 2i/Borisov . Slightly larger than ‘Oumuamua, with a size of about 400–500 meters, Borisov announced that ‘Oumuamua had not been a mere anomaly. The discovery confirmed that interstellar visitors were indeed real, and humanity had the means to detect them.
3I/Atlas: A Colossal Discovery
To emphasize our ability to track interstellar objects, the 3I/Atlas was discovered on July 1, 2025, by telescopes from the Atlas Network in Chile. Upon confirming its hyperbolic trajectory , it was officially named 3I/Atlas. Marking a significant advancement in space observation , this gigantic object dwarfs its predecessors. Initial estimates suggest its diameter is between 5 to 20 kilometers , making it much easier for scientists to study compared to its smaller counterparts.
Speed and Trajectory of 3I/Atlas
3I/Atlas is not just large; it is also extraordinarily fast, traveling at an impressive speed of 58-60 km/s with respect to the Sun. This is significantly quicker than ‘Oumuamua’s 26 km/s and Borisov’s 32 km/s . Its trajectory is also unique; it will reach its closest point to the Sun , known as perihelium, on October 29 , passing between the orbits of Mars and Earth.
Although our planet will be situated on the opposite side of the Sun during this time, making direct observation impossible, 3I/Atlas will be only 31.4 million kilometers away from Mars on October 3 . This proximity presents a captivating opportunity for Mars orbiters, like the Mars Reconnaissance Orbiter , to capture images of this interstellar traveler.
Insights from Interstellar Objects
Each of these interstellar objects serves as a precious time capsule from another solar system. Unlike bodies from our solar system, which share a common origin, these visitors are authentic outsiders . They carry vital clues about the formation and composition of worlds orbiting different stars. Studying them is akin to receiving geological samples from distant corners of the galaxy that would otherwise take millennia to reach.
The Future: ESA’s Mission Interceptor
Until now, our observational abilities limited us to analyzing their fleeting passages. However, this is about to change; the European Space Agency (ESA) is preparing to launch the Mission Interceptor scheduled for 2029 . The mission aims to “park” a probe at a specific point in Lagrange (L2) to await a pristine comet of long periods or even a new interstellar visitor.
This will mark the first rapid response mission aimed at intercepting such mysterious objects. In less than ten years, our understanding has evolved from the mere acknowledgment of their existence to actively planning how to send a spacecraft to explore them. With next-generation observatories like Vera Rubin expected to unearth dozens of interstellar objects in the coming decade, we are embarking on a new era of astronomy. The universe continues to unveil its secrets right in our neighborhood.
Image credit: The interstellar comet 3i/Atlas (ESA)
In conclusion, the progress we have made in detecting and understanding interstellar objects is both exhilarating and humbling. With each new discovery, we deepen our knowledge of the cosmos and our place within it, revealing the mysteries of the universe in ways that were previously unimaginable.