A rare interstellar visitor triggered a SETI search for alien technology

First identified in July 2025, 3I/ATLAS is only the third confirmed interstellar object ever observed entering our Solar System. It follows the discoveries of 1I/’Oumuamua and 2I/Borisov, both of which originated outside our planetary neighborhood.

Because it formed around another star, 3I/ATLAS offers scientists a valuable chance to study material from a different stellar system and gain insights into how planets and planetary systems develop. Although current evidence strongly points to a natural origin, researchers also view interstellar visitors as important targets in the search for technosignatures. In the unlikely event that one of these objects were artificial, it could reveal detectable technology and potentially provide the first evidence of life beyond Earth.

“Eventually, our own Voyager spacecraft will be extraterrestrial artifacts in other stellar systems,” said Dr. Sofia Sheikh, lead author on the paper. “Given that, it is important that we understand the natural distribution of interstellar objects so that we will be able to identify any anomalies that could one day be signs of an artificial interstellar object.”

To investigate that possibility, the team observed 3I/ATLAS for more than seven hours using the ATA. The observations covered frequencies from 1 to 9 gigahertz, a range suitable for detecting narrowband radio transmissions. Such signals are not known to occur naturally and would be considered evidence of technology.

Sorting Through Millions of Signals

During the search, researchers detected nearly 74 million narrowband signals. Most were quickly identified as human-made interference.

After removing signals linked to Earth-based technology and narrowing the search to signals that matched the object’s motion, only about 200 candidates remained. Further analysis showed that every one of those signals originated from technology on Earth or from satellites orbiting our planet.

No Technosignatures Detected

The search uncovered no evidence of extraterrestrial technology. However, the results provide additional support for the conclusion that 3I/ATLAS is a natural object.

The observations also established new limits on the strength of any possible radio transmitter located on or near 3I/ATLAS. Across the frequencies examined, the study ruled out transmissions stronger than roughly 10-110 watts, comparable to the power consumption of a typical household appliance.

“The results from 3I/ATLAS show how realistic it is to detect a signal with the technology we have today,” said Valeria Garcia Lopez, co-author. “That is why it is important to keep searching for technosignatures, even from objects we might not expect to have signals.”

Rapid Response to New Interstellar Discoveries

The study highlights the Allen Telescope Array’s ability to respond quickly when unusual objects are discovered. Observations of 3I/ATLAS began less than 24 hours after the announcement of its discovery, demonstrating how rapidly the system can be deployed.

Beyond the search for intelligent life, observations of interstellar visitors help scientists better understand the physical characteristics of these objects as they travel through the Solar System.

As astronomers continue finding new interstellar objects, each one provides another opportunity to search for technosignatures while expanding our knowledge of both natural and potentially technological phenomena beyond our Solar System.