When 3I/ATLAS swept into our solar system in July 2025 — only the third confirmed interstellar object ever detected — scientists saw a rare opportunity. Researchers at the SETI Institute aimed the Allen Telescope Array in Northern California at the comet-like visitor for seven hours, scanning radio frequencies between 1 and 9 gigahertz for any sign of artificial transmission.
The result was near-total silence from beyond Earth. Of the 74 million narrowband signals detected, every surviving candidate after rigorous filtering — roughly 200 — was ultimately traced to satellites and terrestrial interference. The observations rule out any radio transmitter more powerful than 10 to 110 watts on or near the object, approximately the energy of a household light bulb.
"Establishing the natural distribution of interstellar objects is essential so we can eventually identify any anomalies that suggest artificial origins," said Dr. Sofia Sheikh of the SETI Institute. While no technosignatures were found, the search demonstrated that humanity's detection infrastructure can respond rapidly to interstellar visitors — a critical capability as such objects are expected to appear with increasing frequency.