October 29, 2025 is a date that many astronomers have been waiting for for months. Not for an eclipse or for a new planet discovered, but for a silent guest coming from far away: 3I/ATLASthe third interstellar object ever detected in our solar system.
Discovered in July 2025 thanks to the ATLAS monitoring system in Chile, 3I/ATLAS is not just any comet. Its hyperbolic trajectory tells of a journey that began in another star system. It is as if a fragment of an unknown world had decided to cross our space, allowing itself to be studied — for a short time.
Today, the object reaches the closest point to the Sunabout 203 million kilometers away, between the orbit of Earth and that of Mars. It’s a key moment, what astrophysicists call it periello: a unique opportunity to observe how the body reacts to intense solar radiation, understand what it is made of and perhaps — who knows — discover something surprising.
The moment of truth for scientists and Loeb’s “revelation window”.
According to physicist Avi Loeb, today’s passage could become a “revelation window”a window of revelation. In these hours, terrestrial and space telescopes – including the James Webb Space Telescope – are collecting every possible signal: reflected light, possible variations in the trajectory, emissions of gas or dust.
Loeb, known for having argued that the previous interstellar object ʻOumuamua could be an artificial probe, urges us not to rule anything out:
Even a single anomalous signal — such as a change in brightness or a tail behaving directionally — would be enough to open up new hypotheses about its origin.
Not all scientists agree. The majority believes that 3I/ATLAS is a very particular cometwith a different composition from those of our system. In fact, the first observations show a very high ratio between carbon dioxide and water – about eight times higher than that of a “classical” comet. In practice, it breathes more CO₂ than water vapor, a sign that it could come from an area colder and more distant than any celestial body ever studied.
Because 3I/ATLAS is talked about
There is something profoundly fascinating about this cosmic fragment. It is about 11 kilometers in diameter, much more impressive than ʻOumuamua or 2I/Borisov, and already shows a growing tail visible from the most powerful telescopes. Its surface reflects sunlight unevenly, as if it were covered in different materials — or simply worn down by millions of years of interstellar space travel.
The truth is that, for science, every such object is like a messenger from another world. Every grain of dust or gas emission tells a story: that of a star system we don’t know, of planets perhaps never born or already disappeared. And for the first time, we can observe it almost up close.
In short, October 29th will not change the history of humanity – but it could change the way we look at the universe. Loeb sums it up like this:
If there is even a one percent chance that it isn’t natural, we need to look closer.
Not an alarm, but an extraordinary opportunity
Don’t panic: 3I/ATLAS poses no danger to Earth. Its orbit does not cross ours and, in a few weeks, it will already be traveling towards the outside of the Solar System, returning to the darkness from which it arrived.
For scientists, however, this is a once-in-a-lifetime moment. During its flyby, sensors from all over the world — from those of ESA to the ALMA radio telescope — will be aimed at it. Each data collected will be able to offer new information on the chemistry and physics of interstellar bodies.
Let it be one alien comet or a piece of lost technology3I/ATLAS remains a symbol of how little we still know about our universe. And, above all, how curious we are to find out.
