Scientists are closely examining 100 unusual radio signals that could potentially hint at extraterrestrial intelligence, marking the final chapter of one of the most ambitious alien-hunting projects ever undertaken. The signals were identified from vast datasets collected by the now-collapsed Arecibo Observatory and analysed through SETI@Home, a pioneering global citizen science initiative launched in 1999.
Over more than two decades, SETI@Home enabled ordinary people around the world to contribute to cutting-edge science. More than two million volunteers donated unused processing power from their home computers, helping researchers sift through enormous volumes of cosmic radio data in the search for signs of intelligent life beyond Earth. Although the iconic Arecibo telescope collapsed in 2020, the scientific legacy it enabled continues to shape ongoing searches for alien civilisations.
From Billions of Signals to Just 100 Strong Candidates
According to a 2025 study published in The Astronomical Journal, researchers initially detected more than 12 billion radio signal events. After carefully filtering out natural cosmic phenomena, background noise, and interference caused by human technology on Earth, scientists narrowed the list down to 100 particularly intriguing candidates.
These shortlisted signals are now undergoing further scrutiny using China’s Five-hundred-meter Aperture Spherical Telescope (FAST), currently the world’s most powerful single-dish radio telescope. By re-observing the regions of space where these signals originated, astronomers hope to determine whether any display patterns consistent with an artificial, intelligent source.
Why Scientists Focused on the 21-Centimetre Wavelength
SETI@Home concentrated on radio signals near the 21-centimetre wavelength, a frequency associated with hydrogen—the most abundant element in the universe. This band is widely monitored by astronomers studying the Milky Way and is considered a logical choice for any advanced civilisation attempting interstellar communication.
Researchers note that a technologically sophisticated alien society might deliberately transmit signals in this frequency range, knowing it would be closely watched by other civilisations and capable of travelling vast cosmic distances with minimal distortion.
Millions of Home Computers Powered a Scientific Breakthrough
To cope with the immense volume of data, SETI@Home distributed small software programs to volunteers worldwide. These programs ran quietly in the background, analysing radio data during idle moments on personal computers. What began as a modest experiment quickly grew into a global network spanning over 100 countries, far exceeding initial expectations.
This collaborative effort not only transformed the way large scientific datasets are processed but also demonstrated the power of public participation in advanced research.
No Confirmed Alien Signal—Yet
So far, none of the 100 shortlisted signals has shown definitive evidence of an intelligent, extraterrestrial origin. However, scientists stress that the project has still delivered major scientific value. It has helped establish new sensitivity limits, ruled out certain types of strong alien signals in our cosmic neighbourhood, and provided crucial insights that will guide more targeted and efficient searches in the future.
As researchers continue to refine their methods and harness more powerful instruments, the legacy of SETI@Home and Arecibo remains a cornerstone in humanity’s ongoing quest to answer one of its oldest questions: Are we alone in the universe?