The SETI team recently announced the latest observation results: 3I/ATLAS, a rare celestial object from other star systems, did not reveal any artificial radio signals, supporting that it is an ordinary interstellar comet and not a vehicle made by an alien civilization. The SETI Institute of the United States used the Allen Telescope Array at the Hart Creek Radio Observatory in northern California to conduct a systematic "technosignature" search for the interstellar object 3I/ATLAS.
3I/ATLAS is the third interstellar visitor observed by humans to travel through the solar system, after 1I/ʻOumuamua and 2I/Borisov. After its trajectory and activity characteristics were confirmed in July 2025, it triggered the association of "alien technology" in the astronomical community and the public. SETI scientists use this opportunity to investigate possible artificial radio radiation around it as it passes through the solar system, hoping to search for signs of extraterrestrial civilization.
Previous optical and infrared observations have shown that 3I/ATLAS behaves very much like a conventional comet, including releasing gas and dust, and does not exhibit any unusual propulsion or control characteristics. Despite this, the research team pointed out that such interstellar visitors are still important targets for technological signal searches: if one of them is an artificial celestial body, it may carry detectable communication or navigation signals and provide mankind with the first direct evidence that advanced civilization exists outside the solar system. Sofia Sheikh, the first author of the paper, said that in the future, probes such as the Voyager launched by humans will eventually enter other star systems. From the perspective of alien civilizations, they will also become "interstellar artifacts." Therefore, understanding the distribution characteristics of natural interstellar objects today is crucial to identifying "abnormal targets" in the future.
In specific observations, the research team used the Allen Telescope Array to continuously monitor 3I/ATLAS for more than seven hours, covering a wide frequency band from 1 to 9 gigahertz, focusing on searching for narrowband radio signals. Narrowband signals are extremely rare in nature, and when narrowband radiation is found associated with the motion of celestial bodies, it is often viewed as a possible clue to technological activity. During this process, astronomers recorded a total of about 74 million narrowband signals. Afterwards, through multiple rounds of filtering, the vast majority of signals generated by human radio interference and Earth-orbiting satellite communications were eliminated, leaving only candidate samples that matched the apparent motion trajectory of 3I/ATLAS.
After further verification, all of the approximately 200 candidate signals were determined to originate from ground equipment or earth-orbiting satellites, and no abnormal technical signals related to 3I/ATLAS were found. This result not only negates the possibility of a strong radio transmitter near the object, but also sets a new upper limit for the technological activities that can be hidden around interstellar objects. The research team pointed out that within this frequency band, radio emission sources with a power of approximately 10 to 110 watts or more can be excluded. This energy level is roughly equivalent to the power consumption of ordinary household appliances.
Although they failed to find evidence of extraterrestrial technology, the researchers emphasized that the 3I/ATLAS observations demonstrate that it is feasible for existing instruments to detect potential technological signals under realistic conditions. Co-author Valeria Garcia Lopez said that this is an important reason to continue to carry out technical signal searches: even near seemingly "ordinary" interstellar comets, humans still have the opportunity to capture unexpected signs of civilization. At the same time, this project also demonstrated the rapid response capability of the Allen Telescope Array - from the official announcement of 3I/ATLAS to the start of observations, the interval was less than one day, providing practical experience for handling more sudden interstellar visitors in the future.
In addition to its significance in the exploration of extraterrestrial civilizations, such observations also help scientists deepen their understanding of the natural properties of interstellar matter. As astronomical survey projects continue to progress, the number of discovered interstellar objects is expected to continue to increase. Each one may become a sample for studying the formation and evolution of planetary systems, and it is also a new window for searching for technical signals. The research team believes that with the accumulation of data, humans will gradually establish a "background image" of interstellar visitors, making it easier to identify targets that are truly abnormal and may carry traces of alien technology in the future.
The relevant research is titled "A Search for Radio Technosignatures from Interstellar Object 3I/ATLAS with the Allen Telescope Array" and was published in The Astronomical Journal on June 3, 2026. It provides the latest observational evidence for humans to understand the boundary between the search for interstellar objects and extraterrestrial civilizations.