For over half a century, the astronomers and astrophysicists pursuing the search for extraterrestrial intelligence (SETI) have called it the âwater hole.â The water hole is a quiet little gap in the cosmic background noise between 1.42 and 1.66 GHz, overlapping with the natural microwave-band frequencies emitted and absorbed by hydrogen and hydroxyl molecules, which react to form water.

Researchers have long theorized that our fellow water-loving, carbon-based lifeforms might use this range to broadcastâboth due to these frequenciesâ obvious symbolic implications and because widespread hydrogen and hydroxyl in interstellar gas absorbs the static cosmic noise in this range. The water hole is not only a clear channel for communication, in other words, but one with real poetic resonance.

But SETI scientistsâ infatuation with this notion seems to be fading. New research presented by academics in the UK this Friday instead looks beyond the water hole, focusing on narrow-band signals that may be more likely to come from deliberate, directed transmissions. This new search for concentrated narrow-band emissions, they argue, unlocks âan entirely new frequency window for technosignature detection.â It might even catch âaccidental leakage or relic signals from extinct civilizations.â

âFor 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,â as astronomer Louisa Mason, first author on two studies pursuing this new approach, explained in a statement.

To start their hunt, Masonâs team pored over archived observational data collected by the Atacama Large Millimeter/Submillimeter Array (ALMA), a telescope high in the Chajnantor desert plateau above Chile.

âOne of the most exciting things about this work is realising that weâve surveyed many more stars than initially thought,â Mason said.

Retracing your steps

The beauty of Mason and her colleaguesâ approach is that it offers a new way to reexamine reams of old data that might already have messages from an alien civilization just waiting for us to hear. From ALMAâs archival data, the team surveyed so-called Band 3 information, with a focus on two high-frequency, narrow-band windows around 90.642 and 93.151 GHz, which have wavelengths in the millimeter and submillimeter range.

âThe 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,â according to Mason, who works as a PhD researcher at the University of Manchester in the UK.

The ALMA Band 3 data came with other benefits too. It was collected in very high fidelityâmeaning with high resolution along the electromagnetic spectrumâwhich allowed the team to search for truly narrow-band frequencies between fractions of GHz. In some cases, the data also had a wide field of view, collecting signals from more distant star systems than ALMAâs astronomers had initially intended. Masonâs team calls it âstellar bycatch.â

âEven a very small observation can contain a huge number and diversity of stars that we might never have intended to study,â Mason said.

Maps to the stars

But the teamâs work with ALMA is only the beginning. Thus far, Mason and her partners have also started looking through astronomical data collected by the European Space Agencyâs retired orbital observatory Gaia, for a study published this past January. The team, which includes the SETI Institute in the U.S., delivered a poster presentation on their ongoing progress Friday at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham, UK.

This ongoing work has enhanced the scope of Masonâs narrow-band SETI search by mapping the data to the so-called Besançon Galaxy model of the Milky Way, a data-derived model of our home galaxy built to reproduce the orbits of its many hundreds of billions of stars. Mason says her team has not yet found a confirmed alien signal, but sheâs hopeful itâs on the right track.

âBy combining high-frequency observations with galactic simulations, we can better understand exactly what we’ve searched and where we should look next,â Mason said.