SETI program follows up its final 100 signals with FAST telescope

Astronomers are using China's FAST radio telescope to reobserve 100 candidate narrowband signals flagged by SETI@home; the team expects many may prove to be local radio interference and analysis is ongoing.

Astronomers are using China's Five-hundred-meter Aperture Spherical Telescope (FAST) to reobserve 100 candidate narrowband signals originally flagged by the SETI@home project. SETI@home ran from 1999 to 2020 and used millions of volunteer computers to analyse data collected by the Arecibo radio telescope. Early processing identified about 12 billion candidate signals, and years of automated and manual review have narrowed those down to 100 for targeted follow-up. FAST began follow-up observations in July 2025 because Arecibo collapsed in December 2020, leaving FAST as the only telescope capable of this level of sensitivity. Key facts: - SETI@home used distributed volunteer computing to process Arecibo observations and ran from 1999 until 2020. - Initial processing flagged roughly 12 billion narrowband candidate signals, which were reduced by algorithms and manual inspection to about 100 candidates. - Follow-up observations with the FAST telescope started in July 2025 and remain under analysis. - The SETI team reports that past experience suggests many candidates will turn out to be local radio frequency interference (RFI). - The overall SETI@home results were presented in two papers in The Astronomical Journal in 2025. Summary: The FAST follow-up marks the final stage of a large citizen-science effort and helps establish a new sensitivity benchmark for narrowband SETI searches. If no extraterrestrial source is confirmed among the 100 candidates, the team will report the resulting sensitivity limits; further actions or reanalyses are undetermined at this time.