A radio signal from a star 238 light-years away briefly looked like it might be a sign of alien life, but the astronomers who found it say it’s more likely coming from somewhere on Earth.
The signal turned up in data from China’s FAST (Five-hundred-meter Aperture Spherical Telescope), the world’s largest single-dish radio telescope, which spent several months in 2021 listening for artificial radio signals (technosignatures) from 33 known exoplanet systems.
The initial 2021 survey found nothing beyond a single false alarm toward Kepler-438b (an Earth-sized exoplanet), but the software used at the time could only spot rigid, straight-line frequencies.
To see if any faint or curved signals had been overlooked, a team of SETI (Search for Extraterrestrial Intelligence) researchers led by Zi-Qi Li of Beijing Normal University revisited those recordings in mid-2026 with a new AI-driven signal processing pipeline (known as MSWNet) designed to filter out background radio noise.
Their study entitled ‘A Wavelet-Integrated Search Pipeline for Narrowband Technosignatures in FAST Observations of 33 Exoplanet Systems‘ was published recently in The Astronomical Journal.
Out of more than 139,000 signals flagged by the new software, nearly all were dismissed as interference. Along with re-detecting the known Kepler-438 signal, the AI surfaced just one new candidate of interest.
That candidate, which held up the longest, came from K2-155, a small red dwarf with three planets that are all larger than Earth, one of which orbits close to the habitable zone where liquid water could exist.
The signal in question, now designated NBS 260108, was extremely narrow, with its frequency drifting over time. Moreover, it only showed up when the telescope was aimed directly at K2-155, three telltale characteristics scientists watch for in alien transmitters.
But the team found reasons to doubt its extraterrestrial origin. The signal was much stronger in one polarization channel than the other (meaning the signal appeared strongly in the receiver’s vertical channel but was absent in the horizontal one), and signals like it showed up near three other stars, proving the broadcast did not originate from a single planetary system.
The researchers think Earth-based radio interference or a problem with the telescope’s internal equipment is the most likely cause, although they still don’t know exactly what device created it.
Next, the team plans to analyze raw voltage data across all 19 of the telescope’s beams to calculate the exact source position and definitively rule out interference.
Sources: IOPscience, The Astronomical Journal, NASA Exoplanet Archive, FAST, WION