3I/ATLAS: The Third Interstellar Visitor to Our Solar System The Scientific Explanation.
In July 2025, astronomers made an extraordinary discovery — an object unlike most others drifting through our Solar System. Named 3I/ATLAS, this cosmic traveller is only the third confirmed interstellar object ever observed. Its arrival offers scientists a rare glimpse into materials and chemistry that formed around another star, far beyond our own.
What Is 3I/ATLAS?
The name tells its story.
“3I” means it is the third interstellar object detected (after 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019). The “I” stands for interstellar, and “ATLAS” refers to the Asteroid Terrestrial-impact Last Alert System, the telescope network in Hawaii and Chile that first spotted it on 1 July 2025.
Unlike ordinary comets or asteroids that orbit the Sun, 3I/ATLAS is moving on a hyperbolic path, meaning it is not gravitationally bound to our Solar System. It entered from deep space and will eventually depart forever — a fleeting visitor from the stars.
Why the Discovery Matters
Interstellar objects are incredibly rare. Each one that passes through gives scientists a unique opportunity to study the composition and structure of material formed around other stars.
3I/ATLAS is particularly exciting because its chemical makeup is unusual. Observations from the James Webb Space Telescope suggest its coma — the glowing cloud of gas and dust surrounding it — contains a higher proportion of carbon dioxide than water, hinting that it formed in a much colder, more distant environment than typical Solar System comets.
Understanding these differences can help scientists uncover how planets and star systems evolve across the galaxy. It’s like holding a tiny frozen relic from another world and comparing it with our own.
What We Know So Far
3I/ATLAS is travelling at an astonishing speed on its journey through space. It will not come close enough to Earth to pose any threat, passing at roughly 1.8 astronomical units — almost twice the distance from Earth to the Sun.
Its nucleus, hidden within the surrounding gas and dust, is thought to be less than a few kilometres wide, but precise measurements are difficult. The coma is bright and active, suggesting sublimation of volatile ices as the object warms under sunlight.
A network of powerful observatories, including Hubble, JWST, and the European Southern Observatory, continues to monitor its path and composition as it moves through the Solar System.
The Mysteries That Remain
Despite extensive observation, several questions about 3I/ATLAS remain unanswered. Scientists do not yet know its exact size, mass, or point of origin. Tracking its route back to a specific star system is nearly impossible because of the countless gravitational interactions it would have experienced on its journey.
There is also ongoing research into whether it behaves more like a comet or a fragment of rock — or something entirely new. Some researchers even speculate that studying interstellar objects like 3I/ATLAS could reveal how the earliest building blocks of life might travel between star systems.
A Visitor From the Stars
3I/ATLAS is a gentle reminder that our Solar System is not isolated — it’s part of a much larger galactic neighbourhood where objects, dust, and perhaps even the ingredients of life, drift between the stars.
Although it will soon vanish back into the depths of interstellar space, its brief passage will leave behind data and insights that deepen our understanding of the universe beyond our Sun.
