The search for potential extraterrestrial signals from the interstellar object known as 3I/ATLAS has concluded, with findings that may surprise many. Discovered on July 1, 2025, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Rio Hurtado, Chile, this object, officially designated as C/2025 N1, captured global attention as it sped through our solar system at a remarkable 58 kilometres per second.
As the scientific community eagerly awaited any signs of alien life, the Breakthrough Listen project took significant action. On December 18, 2025, while 3I/ATLAS was making its closest approach to Earth—approximately 270 million kilometres away—the team directed the 100-metre Green Bank Telescope to focus on this interstellar visitor. This search marked the most sensitive radio examination of an interstellar object to date, utilizing a location in the National Radio Quiet Zone, where terrestrial transmissions are heavily restricted.
The telescope scanned across four distinct radio bands (L, S, C, and X), ranging from 1 to 12 GHz. This frequency range is often referred to as the “goldilocks zone” for interstellar communication due to its relative quietness, allowing for the detection of faint signals from deep space. Initial results from the search were intriguing, revealing over 471,000 candidate signals.
Yet, the reality of modern astronomy demands diligence in separating genuine signals from interference. The team undertook a meticulous process of sky localisation and interference analysis. Ultimately, this extensive filtering reduced the count to just nine potential signals. Further scrutiny, however, showed these to be false positives, resulting from terrestrial noise or incorrect scanning targets. The study published on the arXiv preprint server delineated a key conclusion: there were no isotropic continuous-wave transmitters emitting at levels above 0.1 watts from the vicinity of 3I/ATLAS. For context, modern mobile phones typically emit around 1 watt of power, indicating that even a low-powered device would have been detectable.
While the absence of alien signals may disappoint those longing for interstellar communication, the results represent a significant advancement in our capabilities. The authors of the study stated, “There is currently no evidence to suggest that ISOs are anything other than natural astrophysical objects.” The heightened sensitivity of this search has established a new benchmark for future investigations, enhancing our ability to discern authentic cosmic messages from the ambient noise of human technology.
The search coincided with observations of unique cometary behaviour, including a rare “anti-tail” and rhythmic jets suggesting that the nucleus of 3I/ATLAS rotates approximately every 15 hours. As this interstellar traveler continues on its hyperbolic trajectory away from our solar system, the scientific community remains optimistic. With advancements such as the upcoming Square Kilometre Array and improvements in AI processing, researchers are increasingly adept at listening to the cosmic sounds around us, paving the way for future explorations of the universe’s mysteries.
