🔭 SETI delivers its conclusion on interstellar object 3I/ATLAS: extraterrestrial technology or not?

Although the natural origin of the interstellar comet 3I/ATLAS is generally accepted, the SETI Institute team nevertheless listened to it in an attempt to pick up a signal that would reveal extraterrestrial technology.

3I/ATLAS is only the third interstellar object ever spotted in our solar system, after the enigmatic 'Oumuamua in 2017 and comet 2I/Borisov in 2019. Officially discovered on July 1, 2025, by the ATLAS telescope in Chile, this object is moving at a dizzying speed. All observations indicate that it is a normal comet, ejected from its original system by gravitational interactions.


Understanding the natural population of interstellar objects is important for one day recognizing a true artificial craft. As Sofia Sheikh, a researcher at the SETI Institute, reminds us, it is essential to identify any anomaly that could be a sign of an object built by a form of intelligence.

Sheikh's team used the Allen Telescope Array in California to listen to 3I/ATLAS for over seven hours. The goal: to capture narrow-band radio signals, which do not exist in nature. Out of nearly 74 million candidates, they retained about 200 after filtering out human interference. In the end, even those 200 turned out to be emissions from Earth or satellites.

Yet this unsuccessful hunt has valuable merit, as it shows that our instruments are capable of detecting possible artificial signatures, or their absence, even from very far away.

The results, published in The Astronomical Journal, confirm based on observations that 3I/ATLAS is indeed a natural object. They set strict limits on the power of any potential transmitter: nothing stronger than a household appliance (10 to 110 watts) in the observed frequencies. This does not mean, however, that research should stop. Quite the opposite: this study shows that our technology is ready to detect a real signal, if it exists.

Beyond the quest for extraterrestrial life, this work helps us refine our methods. Every interstellar object is an opportunity to learn how to distinguish the natural from the artificial. So, even without aliens, 3I/ATLAS has given us a valuable lesson about our own ability to probe the unknown.

One day, our own Voyager probes may become extraterrestrial artifacts in other star systems.

How does SETI detect extraterrestrial signals?

SETI (Search for Extraterrestrial Intelligence) astronomers listen to the universe with radio telescopes. Their favorite method: looking for narrow-band radio signals, that is, emissions concentrated on a very small range of frequencies. No known natural phenomenon produces this kind of signal, unlike the broad bands emitted by stars or galaxies.

When they point a telescope at a target, scientists capture millions of signals in a few hours. Most come from terrestrial sources: satellites, phones, radars. To eliminate them, they compare the data with readings taken in other directions or at other times. Only signals that are persistent and come from the target itself are retained.

In the case of 3I/ATLAS, the Allen Array recorded 74 million signals. After filtering, only 200 remained, all attributed to human-made interference. This rigorous process helps avoid false positives, even though no evidence of extraterrestrial intelligence has yet been found.

Why do interstellar comets come to visit us?

Interstellar comets like 3I/ATLAS are remnants of planetary system formation. When a star is born, it leaves behind a disk of gas and dust where planets and small bodies form. Over time, comets can be ejected from their system by the gravitational forces of giant planets.

These solitary wanderers then drift through interstellar space for millions, even billions of years. Their trajectories become random, and they sometimes happen to cross paths with another star. Our solar system has already hosted three, but it is estimated that hundreds of interstellar objects brush past us each year without being detected.

Studying these visitors helps us understand the composition of other planetary systems. Comet 3I/ATLAS, for example, shows activity similar to that of our own comets, indicating that formation processes are universal.