Researchers at the University of Manchester have proposed that the search for extraterrestrial intelligence should be extended far beyond the narrow radio band that has dominated SETI programs for decades. The recommendation, presented at the National Astronomy Meeting in Birmingham, is backed by what the team describes as the first SETI analysis ever carried out with archival data from the Atacama Large Millimeter/submillimeter Array, known as ALMA.
Historically, radio SETI surveys have concentrated on a frequency window between 1.42 and 1.66 gigahertz, a region of the spectrum known as the water hole. The lower edge of this window coincides with the famous 21-centimeter line emitted by neutral hydrogen, the most abundant element in the universe, while the upper edge includes the main emission lines of the hydroxyl radical OH. Because hydrogen and hydroxyl combine to form water, a molecule essential to life as we know it, scientists have long reasoned that an advanced civilization might recognize this interval as a universally meaningful channel and choose it for communication. The name water hole is an analogy to a watering hole where animals gather to drink, imagined as a symbolic meeting place for intelligent species.
The new study challenges that assumption by exploring frequencies well beyond the traditional listening window. Louisa Mason, a researcher at the University of Manchester who presented the work at the National Astronomy Meeting, said the project was designed to test what might be missed by looking only where SETI has always looked. «For decades, SETI searches have concentrated on a relatively small part of the radio spectrum,» Mason said. «We wanted to ask what could happen if we looked elsewhere. The millimeter and submillimeter radio bands remain almost completely unexplored for SETI, so this is really opening a new area of the search parameter space.»
To test the idea, the team turned to data collected by ALMA, a radio interferometer made up of 66 antennas located on the Chajnantor plateau in Chile's Atacama Desert. The researchers analyzed observations made in band 3, a frequency range normally used to study gas, dust, molecules, and star-forming regions. The analysis targeted narrowband radio signals, a type of emission considered a plausible artificial technosignature because natural astrophysical processes tend to produce radiation spread over much wider frequency ranges. The team examined two spectral windows centered at 90.642 and 93.151 gigahertz in archival data and found no candidate technosignatures above the detection threshold.
According to the researchers, that negative result does not imply the absence of intelligent civilizations. It indicates only that, within the limited frequency windows examined in this study, no compatible signal was detected. Although the investigation covered just four archival observations, the team said the work demonstrates that high-frequency radio telescopes can become valuable instruments for future SETI searches.
The study also offers a new way of measuring how much of the galaxy has actually been surveyed. Whenever a telescope points at a target, many other stars inevitably fall within its field of view, a phenomenon the researchers call stellar bycatch. In the past, studies estimated this bycatch using star catalogs from missions such as Gaia. In this project, the team instead used the Besançon galactic model, a code that estimates the entire stellar population in each observation, including stars too faint, too distant, or not reliably identified in existing catalogs.
Applying that method to a previous SETI survey consisting of 1,327 telescope pointings, the estimated number of stars actually included in the search rose from about 288,000 identified through Gaia to more than 6.1 million using the model. The researchers say this provides a far more realistic picture of the portion of the Milky Way already explored for technosignatures.
Mason described the broader stellar estimate as one of the most exciting aspects of the work. The combined results, she said, point to a clear path forward: extending SETI searches into previously neglected high-frequency bands and using the full field of view of modern observatories to maximize the number of stars examined in a single pointing. The findings were presented during the National Astronomy Meeting, organized from July 20 to 24, 2026, in Birmingham by the Royal Astronomical Society.
