SETI finds no radio signs of technology from 3I/ATLAS

The SETI Institute spent 7.25 hours listening across 1 to 9 gigahertz for radio signs of technology from 3I/ATLAS and found none. Using the Allen Telescope Array at Hat Creek Radio Observatory in Northern California, researchers reduced nearly 74 million narrowband hits to 211 candidates, then traced every one to human-made interference or Earth-orbiting satellites.

3I/ATLAS is the third confirmed interstellar object ever observed, after 1I/'Oumuamua and 2I/Borisov. The ATLAS survey telescope in Rio Hurtado, Chile, first reported it to the Minor Planet Center on July 1, 2025. The object travels on a hyperbolic path, moving too fast to be bound to the Sun, with an icy nucleus and coma consistent with a comet.

The SETI team aimed the Allen Telescope Array at 3I/ATLAS in early July 2025, within days of discovery, and searched for narrowband radio transmissions that could hint at technology. After blanking out radio-frequency interference, the dataset fell from about 74 million detections to roughly 2 million, then to 211 visually inspected hits. None survived follow-up, and the paper set an upper limit on possible radio technosignatures of about 10 to 110 watts EIRP across the surveyed frequencies.

Sofia Z. Sheikh, the study’s lead author, said the broader value of the work was in establishing a baseline for natural interstellar objects. She said that, eventually, human spacecraft could become “extraterrestrial artifacts” in other star systems.

NASA estimates 3I/ATLAS has a nucleus between 440 meters and 5.6 kilometers across, and reached perihelion on Oct. 30, 2025, about 1.4 AU from the Sun. Breakthrough Listen has also found no technosignatures in its wider campaign on the object.