When 3I/ATLAS was discovered on July 1, 2025, it became only the third object ever confirmed to have come from another star system, after ‘Oumuamua in 2017 and Borisov in 2019. Harvard astronomer Avi Loeb argued it could be artificial. Most astronomers saw a comet, and other observations found the dust, gas and organic molecules typical of one.

Scientists at the SETI Institute checked anyway. Less than a day after the discovery was announced, they pointed the Allen Telescope Array, a network of radio dishes in Northern California, at the object. Over more than seven hours, they scanned frequencies from 1 to 9 gigahertz for narrowband signals, which nature doesn’t produce and which would point to technology.

The results were published on June 3, 2026, in The Astronomical Journal. The team identified nearly 74 million narrowband signals. After removing human interference and filtering for signals that moved along with 3I/ATLAS, about 200 remained for review. All of them traced back to technology on Earth or to our own satellites. The search ruled out any transmitter on or near the object stronger than roughly 10 to 110 watts, about the power of a household appliance.

Lead author Sofia Sheikh said that understanding the natural population of interstellar objects is what will let scientists spot a real anomaly someday. Co-author Valeria Garcia Lopez said the result shows how realistic it is to detect a signal with current technology.