For more than 60 years, scientists have searched the skies for signs of intelligent life beyond Earth.
Much of that search has focused on listening for radio signals that might have been created by advanced civilizations.
But new research suggests we may have been searching in only a small part of the radio spectrum, leaving many possible signals unheard.
The study, presented at the Royal Astronomical Society’s National Astronomy Meeting (NAM 2026) in Birmingham, explores a new way to search for possible alien technology by using higher radio frequencies that have received very little attention in previous SETI projects.
SETI, which stands for the Search for Extraterrestrial Intelligence, has traditionally concentrated on radio frequencies between 1.42 and 1.66 gigahertz. This part of the radio spectrum is often called the “water hole.”
It lies between the natural radio signals produced by hydrogen and hydroxyl, two substances that combine to form water.
Because water is considered essential for life as we know it, scientists have long believed that other intelligent civilizations might recognize the importance of this region and choose it as a natural place to send messages.
However, researchers now believe it may be time to widen the search.
Louisa Mason, a doctoral researcher at the University of Manchester, carried out the first SETI survey using the Atacama Large Millimeter/submillimeter Array (ALMA), a powerful group of radio telescopes located high in the mountains of Chile.
Instead of collecting new observations, Mason examined data that had already been gathered for other astronomy projects.
She searched for very narrow radio signals that could stand out from naturally occurring radio waves. Such narrow signals are often considered possible signs of technology because natural objects usually produce radio emissions across much wider ranges of frequencies.
The search focused on two small frequency ranges within ALMA’s Band 3 observations. No possible alien signals were found above the detection limits. While that may sound disappointing, the researchers say the result is still important because it proves that these higher radio frequencies can be searched effectively.
The study also uncovered another surprising discovery. Every time a radio telescope points toward one object in space, it also captures many other stars within its field of view. These additional stars are usually not the main targets of the observation, but they are still being searched at the same time.
Previous studies estimated the number of these extra stars using the Gaia space telescope’s catalog of known stars. Mason instead used the Besançon Galactic Model, a computer simulation that estimates the full stellar population of our galaxy, including stars that are too faint or too distant to appear in current catalogs.
The difference was remarkable. When Mason applied this method to an earlier SETI survey involving 1,327 telescope observations, the estimated number of stars included in the search increased from about 288,000 to more than 6.1 million.
This finding suggests that scientists have actually examined a much larger portion of the Milky Way than previously realized, even if many of those stars were only included by chance.
Researchers stress that not finding a signal does not mean intelligent life does not exist elsewhere in the universe. It simply means no convincing evidence was found within the small areas of the radio spectrum examined in this study.
The work highlights the value of exploring new radio frequencies and making better use of existing telescope data.
By searching across a wider range of the radio spectrum and recognizing the hidden opportunities in archived observations, scientists hope future SETI projects will have a better chance of detecting a signal if one is out there waiting to be heard.
