The Allen Telescope Array tracked the third known interstellar object for more than seven hours, scanning frequencies from 1 to 9 gigahertz. After filtering through some 74 million initial detections, 211 candidates were tested, but all turned out to be interference originating from Earth or satellites.
Researchers from the Institute S Complete another search radio signals Artificial, possibly originating from3I/ATLAS, the third interstellar object discovered to pass through the solar system. Although all astronomical observations indicate that it is a natural comet, researchers wanted to take advantage of the rare opportunity to see if it produces Technology signatures Any.
To do this, the researchers monitored 3I/ATLAS for 7.25 hours using Allen Telescope Array at the Hat Creek Radio Observatory in Northern California. They scanned a wide frequency range, from 1 to 9 gigahertz, looking for extremely narrow radio signals, which in some cases may indicate technological activity. The search did not find a signal originating from extraterrestrial technology. ([arXiv][1])
The third visitor from another star system
3I/ATLAS was discovered in July 2025. Its orbit showed that it was not bound by the Sun's gravity and that it came from interstellar space, having previously been ejected from another star system.
This is the third confirmed interstellar object to be observed in the Solar System. It was preceded by 1I/ʻOumuamua, discovered in 2017, and comet 2I/Borisov, discovered in 2019. Such objects give astronomers a rare opportunity to study material formed outside the solar system, around other stars.
The 3I/ATLAS observations have shown activity consistent with a natural comet, and no features have been found to warrant an artificial explanation. Nevertheless, SETI researchers argue that interstellar visitors are worthy targets for searching for technological signatures precisely because they are not from the solar system. ([SciTechDaily][2])
The Voyager spacecraft launched by humanity in 1977 will also continue to travel in interstellar space in the distant future. From the perspective of an observer in another solar system, they will be artificial objects that have arrived from outside. By the same logic, there is no fundamental obstacle to another technological civilization launching probes to neighboring star systems.
This is not to say that 3I/ATLAS is a probe. The search is intended to test the possibility scientifically, rather than just speculate.
Approximately 74 million initial detections
The researchers were looking for narrowband radio signals. Such signals concentrate their transmission power in a very narrow frequency range, unlike most astrophysical radio sources, which emit over a wider range of frequencies.
In the first phase, the processing system identified almost 74 million narrowband detections. The large number does not indicate millions of mysterious transmissions. Most detections in SETI searches are caused by human radio interference: communication systems, radar, telephones, ground transmitters and satellites.
The researchers first filtered out frequencies and frequency change rates that were typical of known disturbances. This narrowed the list down to about two million detections. Then, they used location software to check whether the signal came from the direction of 3I/ATLAS and did not appear simultaneously in other parts of the sky.
After filtering, 211 candidates remained for manual examination. The researchers examined the evolution of each signal over time and frequency, but found no signal that warranted further observation. The examination showed that the remaining candidates originated from terrestrial technology or from satellites orbiting the Earth. ([arXiv][1])
Why is the signal expected to change frequency slightly?
When a radio signal source moves relative to a telescope, the measured frequency changes due to the Doppler effect. The change is similar to the change in the sound of a passing car horn, but in this case it occurs at radio frequencies.
The rotation of the Earth, the movement of the telescope, the orbit of the object, and the possible movement of a transmitter on it also cause a gradual drift in frequency. Therefore, a SETI search is not satisfied with a constant signal, but looks for signals whose frequency changes at a rate that matches the movement of the target.
The researchers compared the drift rate of each candidate to the expected motion of 3I/ATLAS. This matching was one of the key steps in separating a possible signal from the object itself from thousands of local sources of interference.
What does the 10 to 110 watt limit mean?
The lack of detection allows the researchers to determine the weakest transmitter the system could detect under the observation conditions. According to calculations, the observations were sensitive to a transmitter with an equivalent isotropic radiant power of about 10 to 110 watts, depending on its frequency and rate of change.
This is the power consumption of a small household appliance. The high sensitivity was made possible because 3I/ATLAS was very close to stars and planets outside the solar system. ([arXiv][1])
However, the result does not rule out any possible technology. It only applies to signals in the frequency range tested, at the time the observations were made, and within the range of drift rates the researchers were looking for. A switched-off transmitter, a fragmented signal, a beam not directed at Earth, or communications based on a different technology would not necessarily be detected.
Non-detection is not proof that there is no intelligent life.
The study does not attempt to prove that there is no intelligent life outside Earth. It states something much more limited: At the time of the observations, no radio transmitter was found near 3I/ATLAS that matched the conditions the researchers tested.
This is an important distinction in SETI searches. Each observation examines only a small part of the space of possibilities: a certain range of frequencies, intensities, times, locations, and types of signals. Non-detection helps narrow down the possibilities, but it does not rule out the very existence of extraterrestrial technology elsewhere.
The importance of the search is also methodological. The Allen Telescope Array team began observing 3I/ATLAS less than 24 hours after its discovery was announced. This demonstrates the ability to respond quickly to the discovery of a new interstellar object and conduct a focused search while it is still observable. ([SciTechDaily][2])
Preparing for the next visitors
As sky survey systems improve, astronomers are expected to discover Interstellar objects Additional. The Vera Rubin Observatory, which has begun a broad and ongoing survey of the southern skies, may greatly increase the number of visitors to be discovered in the coming years.
Any such object would be a prime source of information about the formation of other planetary systems. Its chemical composition, dust, ice, and gases could teach us how comets and planets formed around distant stars.
At the same time, the researchers suggest that searches for technological signatures should become a routine part of tracking interstellar objects. In most cases, the expected result will be completely natural, as happened with 3I/ATLAS. However, conducting a systematic examination allows us to identify a real anomaly, if it is ever discovered, and to distinguish it from radio interference, satellites, or natural phenomena that are not yet understood.
The current search did not find extraterrestrial technology. It did show that, using existing telescopes and processing systems, it is possible to examine a visitor from another star system quickly and with high sensitivity – and replace speculation with measurement.
The scientific article
“A Search for Radio Technosignatures from Interstellar Object 3I/ATLAS with the Allen Telescope Array,” by Sofia Z. Sheikh, Valeria Garcia Lopez, and colleagues. Published in The Astronomical Journal on June 3, 2026. DOI: 10.3847/1538-3881/ae6651. ([SciTechDaily][2])
For the scientific article: Opening the scientific article
More on the subject on the science website
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- Alien ice or cosmic relic? Scientists wonder about chilling discovery in deep space
- Are alien spacecraft hiding in the solar system? New study claims: We've barely looked
- The visitor from outside the solar system is almost as old as the galaxy itself
- Molecular templates that will help identify extraterrestrial life forms will be used in the next spacecraft in the solar system
