NORTHERN CALIFORNIA — The SETI Institute's Allen Telescope Array in Northern California observed interstellar Comet 3I/ATLAS in July 2025, finding no evidence of artificial radio signals. Researchers detected approximately 74 million narrowband signals during the observation period, all of which were traced to Earth-based sources or orbiting satellites.
Astronomers first detected Comet 3I/ATLAS on July 1, 2025, using a remote telescope operated by the Asteroid Terrestrial-impact Last Alert System in Chile. A NASA-funded asteroid impact warning system identified the object entering the solar system from interstellar space. NASA designated it Comet 3I/ATLAS and stated it does not pose a threat to Earth.
Comet 3I/ATLAS represents the third confirmed interstellar object detected in the solar system, following previous detections in 2017 and 2019. The discovery prompted online discussions about the possibility that the object could be extraterrestrial technology. The Hubble Space Telescope captured an image of Comet 3I/ATLAS on July 21, 2025, when it was 277 million miles from Earth.
The institute team collected over seven hours of data across a frequency spectrum of 1 to 9 gigahertz. The study findings were published in The Astronomical Journal. The institute stated, "While observations strongly indicate that 3I/ATLAS is a natural object, interstellar visitors are also compelling technosignature targets because an artificial object — however unlikely — could represent detectable extraterrestrial technology and potentially provide the first evidence of life beyond Earth."
Valeria Garcia Lopez, an institute researcher, said, "The results from 3I/ATLAS show how realistic it is to detect a signal with the technology we have today. That is why it is important to keep searching for technosignatures, even from objects we might not expect to have signals." Another institute researcher, Sofia Sheikh, said, "Eventually, our own Voyager spacecraft will be extraterrestrial artifacts in other stellar systems. 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."