The recent interstellar object known as 3I/ATLAS has been confirmed to produce nine radio signals that researchers have identified as human-made noise rather than signs of extraterrestrial intelligence. Discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii, 3I/ATLAS garnered significant attention due to its unbound trajectory, indicating it originated from outside the Solar System.
While some scientists, including Harvard astrophysicist Avi Loeb, speculated about the possibility of technological probes being among such interstellar visitors, many experts urged caution. They emphasized the importance of focusing on accurate measurements and scientific data over sensational claims that could detract from legitimate research. This ongoing debate helped elevate 3I/ATLAS to a prominent position on the observational agenda as it approached the inner Solar System.
During its flyby, the comet never came closer than approximately 270 million kilometers from Earth, a safe distance that allowed powerful radio telescopes to monitor its activity. The Breakthrough Listen initiative seized this opportunity to conduct a focused search for potential ‘technosignatures,’ or radio signals that might indicate artificial origins. On December 18, 2025, less than 24 hours before the comet’s closest approach, the team utilized the 100-metre Green Bank Telescope in West Virginia to sweep frequencies from 1 to 12 gigahertz, including the so-called ‘water hole’—a quiet area of the radio spectrum often considered a logical location for intelligent communication.
In concert with the Green Bank Telescope, the Allen Telescope Array in California and other collaborating observatories gathered complementary data, crafting one of the most comprehensive technosignature surveys ever conducted for an interstellar object. The campaign yielded nine radio signals that initially appeared promising, characterized by sharp spikes in specific frequencies. However, upon further examination, researchers discovered that these signals emerged when the instruments were not aimed at 3I/ATLAS, indicating interference from human technology on or near Earth.
After an in-depth analysis, the team concluded that all nine signals were merely human-made radio noise, likely caused by passing satellites, aircraft transmitters, and ground-based communication systems that frequently interfere with deep-space observations. In a paper pending peer review, the researchers stated bluntly: “Like those searches, we find no credible detections of narrowband radio technosignatures originating from 3I/ATLAS.” They noted that similar investigations in 2025 by other teams utilizing different telescopes and frequency ranges also failed to yield any evidence of artificial signals.
Although the findings do not definitively prove that 3I/ATLAS is entirely natural, the researchers asserted that each non-detection helps refine the parameters for future searches for potential extraterrestrial communication. They suggested that if a non-human probe were attempting to communicate across interstellar distances, narrowband radio would likely be the medium, similar to the methods employed by Voyager 1 and Voyager 2 in transmitting data back to Earth.
In tandem with the technosignature search, another team focused on the dynamics of 3I/ATLAS as it interacted with the Sun. They investigated its non-gravitational acceleration—an effect experienced by comets when sunlight vaporizes ice, creating jets that act as natural thrusters. By analyzing this alongside estimates of the material being lost, they determined that the nucleus of 3I/ATLAS is approximately one kilometre in diameter, consistent with the size of familiar Solar System comets. They found no signs of unusual reflectivity, erratic tumbling, or sudden brightness changes that might indicate artificial constructs or maneuvers.
Their findings led them to conclude that “3I/ATLAS exhibits mostly typical cometary characteristics,” stating, “There is currently no evidence to suggest that ISOs are anything other than natural astrophysical objects.”
As 3I/ATLAS drifts away into the depths of space, it serves as a reminder that natural phenomena can be both captivating and complex, independent of extraterrestrial influence. The extensive efforts dedicated to studying this brief visitor highlight the seriousness with which astronomers approach even the slightest possibility of detecting signs of other civilizations. The nine radio signals, while not indicative of life beyond Earth, have refined the tools and methods for future investigations.
In order to yield clearer results with the next interstellar arrival, continued support for ambitious initiatives such as Breakthrough Listen is essential, along with enhanced protection of the radio spectrum from interference and ongoing public interest in meticulous, data-driven astronomy.
