Summary
Presented at the Royal Astronomical Society’s National Astronomy Meeting 2026 (NAM 2026, Birmingham), this study by louisa-mason, a University of Manchester doctoral researcher, conducted the first SETI survey using archival ALMA data. Rather than the traditional 1.42–1.66 GHz “water-hole” band used by most radio SETI surveys, Mason searched two frequency windows in four archived ALMA Band 3 (millimeter/submillimeter) observations, finding no candidate technosignatures above detection thresholds. She argues the null result nonetheless demonstrates that high-frequency telescopes are viable SETI instruments and that millimeter/submillimeter parameter space remains almost entirely unexplored. Separately, Mason introduced a “stellar-bycatch” method using the Besançon Galactic Model — rather than the Gaia catalog — to estimate the full stellar population incidentally captured within telescope pointings; applied to a prior 1,327-pointing SETI survey, it raised the estimated surveyed-star count from ~288,000 (Gaia) to over 6.1 million.
Key Claims
- Most radio SETI surveys concentrate on the 1.42–1.66 GHz “water hole,” between the hydrogen and hydroxyl emission lines (Mason).
- This is the first SETI survey to use ALMA, analyzing archival Band 3 data originally collected for other astronomical purposes (Mason).
- Two frequency windows searched across four archived ALMA observations; no candidate technosignatures found (Mason).
- “The millimeter and submillimeter radio bands remain almost completely unexplored for SETI” (Mason).
- Every telescope pointing incidentally captures many non-target “bycatch” stars; the Besançon Galactic Model estimates this population more completely than Gaia, which misses faint, distant, or crowded-field stars (Mason).
- Retrofitting the bycatch method onto a prior 1,327-pointing survey raised the estimated surveyed-star count from ~288,000 (Gaia) to over 6.1 million (Besançon model) (Mason).
- A null result does not mean intelligent life doesn’t exist — only that no signal was found in the narrow frequency ranges examined (Mason).
Notable Quotes
“For decades, SETI searches have concentrated on a relatively small part of the radio spectrum. We wanted to ask what might happen if we looked somewhere very different.” — Louisa Mason
“The millimeter and submillimeter radio bands remain almost completely unexplored for SETI, so this is really about opening up a new area of parameter space to search.” — Louisa Mason
“One of the most exciting things about this work is realizing that we’ve surveyed many more stars than initially thought.” — Louisa Mason