Astronomers Identify Nine Signals from 3I/ATLAS as Human Noise

Researchers have determined that nine radio signals detected during the flyby of the interstellar object 3I/ATLAS are likely the result of human interference. Initially observed on July 1, 2025, 3I/ATLAS piqued interest due to its classification as the third known interstellar object to enter our Solar System. Discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Hawaii, the object is confirmed to be unbound to the Sun, indicating it originated from outside our planetary system.

The discovery of 3I/ATLAS quickly ignited discussions among scientists regarding the potential for technologically advanced probes among interstellar visitors. Notable astrophysicist Avi Loeb advocated for considering non-natural origins for such objects. Others cautioned against jumping to conclusions, emphasizing the need for careful data collection and analysis.

During its passage through the inner Solar System, 3I/ATLAS maintained a distance of approximately 270 million kilometers from Earth, which allowed astronomers to employ powerful radio telescopes to monitor its movement and activity. The Breakthrough Listen initiative, dedicated to searching for signs of extraterrestrial communication, capitalized on this opportunity to conduct a focused search for potential technosignatures—signals indicative of artificial origins.

On December 18, 2025, less than a day before its closest approach, the Green Bank Telescope in West Virginia was directed to observe 3I/ATLAS. The team meticulously swept frequencies between 1 and 12 gigahertz, including the so-called “water hole,” a relatively quiet section of the radio spectrum where intelligent civilizations might choose to broadcast. Simultaneously, the Allen Telescope Array in California and other facilities collected complementary data, contributing to one of the most comprehensive surveys of technosignatures related to an interstellar object.

Despite the anticipation, the results revealed that the nine radio events flagged for further analysis were not groundbreaking. Each signal appeared as a distinct spike in the radio spectrum, which initially suggested potential technosignatures. However, upon further investigation, researchers found that these signals coincided with periods when the telescope was not aimed at 3I/ATLAS, indicating interference from human-made sources such as satellites, aircraft transmitters, and terrestrial communication systems.

In a paper awaiting peer review, the team summarized their findings, stating, “Like those searches, we find no credible detections of narrowband radio technosignatures originating from 3I/ATLAS.” They noted that similar surveys conducted by other teams in 2025, utilizing different telescopes and frequency ranges, also failed to yield significant results.

While the absence of confirmed technosignatures does not definitively prove that 3I/ATLAS is of natural origin, researchers argue that each non-detection narrows the possibilities for future investigations. If non-human probes exist, they assert that narrowband radio signals would be a likely choice for communication, akin to how the Voyager 1 and Voyager 2 spacecraft transmit data to Earth.

In addition to the search for technosignatures, another group of scientists investigated the dynamics of 3I/ATLAS as it interacted with the Sun. They examined its non-gravitational acceleration, a phenomenon where sunlight heats the comet, causing gas to escape and create jets that function as natural thrusters. This analysis revealed that 3I/ATLAS has a solid nucleus approximately one kilometer in diameter, consistent with the size range of known comets in our Solar System. The study found no anomalies in reflectivity or brightness that might suggest artificial structures, leading the team to conclude that “3I/ATLAS exhibits mostly typical cometary characteristics.”

As 3I/ATLAS continues its journey away from the Solar System, it joins previous interstellar objects as a testament to the natural wonders of the cosmos. The extensive efforts surrounding this transient visitor highlight the seriousness with which astronomers approach the search for extraterrestrial life. Each quiet outcome contributes to refining methodologies for identifying potential signals from other civilizations.

In the wake of this investigation, researchers emphasize the importance of continued support for ambitious projects like Breakthrough Listen, improved protection of the radio spectrum from interference, and sustained public interest in meticulous, data-driven astronomy. As the scientific community prepares for future interstellar visitors, the tools and techniques honed during this campaign will be invaluable in the ongoing quest for clarity in the search for life beyond our planet.