100 Unexplained Signals From Space Still Baffle Scientists After Decades of Searching

A decades-long search for signs of intelligent life beyond Earth has left scientists with 100 unexplained signals. These candidates emerged from billions of anomalies flagged by SETI@home, a groundbreaking project that harnessed the power of volunteers' computers. The effort, which ran from 1999 to 2020, analysed data from the now-collapsed Arecibo Observatory in Puerto Rico.

SETI@home launched in 1999 with a simple but ambitious goal: to scan radio telescope data for potential technosignatures—signals that might indicate extraterrestrial intelligence. Within days, 200,000 users had signed up to donate their computers' idle processing time. A year later, that number surged to 2 million, proving how public enthusiasm could accelerate scientific research.

The project sifted through vast amounts of data from the Arecibo Observatory, one of the world's most powerful radio telescopes at the time. Over its 21-year run, SETI@home identified roughly 12 billion unusual signals. Most were dismissed as interference or natural phenomena, but 100 remained intriguing enough for further study.

In 2020, six years after SETI@home stopped distributing new data, its final findings were published in The Astronomical Journal. The paper highlighted the 100 persistent candidates, prompting follow-up observations. China's FAST telescope, now the world's largest, took on the task of re-examining these signals. By February 2026, none had been confirmed as extraterrestrial in origin, though a handful—including candidates 57 and 72—received extra attention in studies between 2021 and 2023.

The project's legacy endures despite the loss of Arecibo, which collapsed in 2022. Its success demonstrated how distributed computing could turn a global network of volunteers into a force for scientific discovery.

The 100 signals remain under investigation, with FAST continuing to monitor them for any unusual patterns. While none have yet been verified as proof of alien technology, the search highlights both the challenges and potential of crowdsourced science. The data collected by SETI@home still offers a foundation for future research into the possibility of life beyond Earth.