For decades, the search for extraterrestrial intelligence has quietly agreed on where to listen. Most radio SETI surveys train their instruments on frequencies between 1.42 and 1.66 gigahertz, a band nicknamed the “water hole” because it sits between the natural radio emissions of hydrogen and hydroxyl — two molecules that combine to form water. The logic has always been elegant: a technologically capable civilization might recognize the symbolic significance of that chemistry and choose to transmit, or listen, right there. New research presented this week at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham suggests that decades of consensus may have left an entire region of the radio spectrum essentially unexamined.
The work comes from Louisa Mason, a PhD researcher at the University of Manchester, who carried out what is described as the first-ever SETI survey conducted using the Atacama Large Millimeter/submillimeter Array, or ALMA, in Chile. Rather than booking new telescope time, Mason mined archived ALMA observations that had originally been collected for unrelated astronomical purposes, scanning them for narrowband radio signals — the kind of signal associated with technology rather than natural astrophysical processes.
“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,” Mason said. “The millimetre and submillimetre radio bands remain almost completely unexplored for SETI, so this is really about opening up a new area of parameter space to search.”
Mason focused on two narrow frequency windows within ALMA’s Band 3 observations. She found no candidate technosignatures above the survey’s detection thresholds — and with only four archived observations examined, the search itself was modest in scope. But Mason argues the value of the work lies less in what it found than in what it demonstrates is possible: that high-frequency radio telescopes, largely absent from SETI efforts to date, could play a meaningful role in future searches.
The project also surfaced a second, less expected finding — one about how astronomers have historically counted their own search coverage. Whenever a radio telescope points at a single target, it inevitably captures many other stars sitting within its field of view, a phenomenon researchers call “stellar bycatch.” Traditionally, scientists have estimated the size of that incidental haul using star catalogues such as Gaia. Mason instead used the Besançon Galactic Model, a statistical simulation of the galaxy’s stellar population, to estimate the full range of stars captured in each observation — including stars too distant, too dim, or too poorly resolved to appear reliably in existing catalogues.
Applied to a previous SETI survey covering 1,327 telescope pointings, the shift in method was dramatic: the estimated number of stars swept up in the search jumped from around 288,000, based on Gaia’s catalogue, to more than 6.1 million using the galactic model. “One of the most exciting things about this work is realising that we’ve surveyed many more stars than initially thought,” Mason said. “Even a very small observation can contain a huge number and diversity of stars that we might never have intended to study. By combining high-frequency observations with galactic simulations, we can better understand exactly what we’ve searched and where we should look next.”
Mason is careful to note what the null result does and doesn’t mean. The absence of a detected signal in this study says nothing definitive about whether intelligent life exists elsewhere — it only confirms that no candidate signal turned up within the narrow frequency ranges this particular survey examined. Her hope is that the work nudges future SETI efforts toward a wider swath of the radio spectrum, and toward making fuller use of astronomical data that already exists in observatory archives rather than waiting on dedicated new observing time.
That archival approach carries practical appeal for a field that has always had to compete for scarce and expensive telescope time. If meaningful SETI science can be extracted from data collected for entirely different research questions, the pool of usable observations expands enormously — encompassing years of accumulated ALMA data and, by extension, similar archives at other high-frequency observatories that have never been mined with alien signals in mind.
The research was conducted in collaboration with Professor Michael Garrett, Dr. Andrew Siemion, and Dr. Kelvin Wandia, and builds on Mason’s earlier published work modeling both high-frequency SETI strategies and the stellar bycatch problem. Together, the studies make the case that the water hole’s decades-long hold on SETI strategy may say more about historical convention than about where a genuine signal is most likely to be found — and that the next candidate detection could just as easily turn up in a frequency band astronomers have barely thought to check.
Endnotes
1. Mason, L. A., et al. “Strategies Utilising High-Frequency Interferometric Data to Explore SETI Parameter Space.” Presented at the Royal Astronomical Society’s National Astronomy Meeting 2026, Birmingham.
2. Mason, L. A., Garrett, M. A., Siemion, A. P. V. “Simulating the stellar bycatch: constraining the prevalence of extraterrestrial transmitters within radio SETI surveys.” Monthly Notices of the Royal Astronomical Society, Vol. 545, Issue 3 (2026). DOI: 10.1093/mnras/staf2112
3. Mason, L. A., Garrett, M. A., Wandia, K., Siemion, A. P. V. “Conducting high-frequency radio SETI searches using ALMA.” Monthly Notices of the Royal Astronomical Society, Vol. 536, Issue 3 (2025). DOI: 10.1093/mnras/stae2714
4. Royal Astronomical Society press release, July 23, 2026, via EurekAlert!: https://www.eurekalert.org/news-releases/1137101
