Astronomers searching for intelligent life beyond Earth may be overlooking potential technosignatures because most radio SETI projects focus on a relatively narrow range of frequencies.
For decades, radio SETI (Search for Extraterrestrial Intelligence) programs have primarily examined frequencies between 1.42 and 1.66 GHz. This region is known as the “cosmic water hole” because it lies between the natural radio emissions of hydrogen and hydroxyl, the two components of water.
Scientists have suggested that this relatively quiet part of the radio spectrum could be a logical location for interstellar communication. An advanced civilization might recognize the significance of hydrogen and hydroxyl and intentionally transmit or monitor signals within this range.
Expanding the Search Beyond the Cosmic Water Hole
New research suggests that higher radio frequencies could provide another promising region for detecting technological signals from distant civilizations. The findings are being presented this week at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham.
Louisa Mason, a PhD researcher at the University of Manchester, used archived observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to conduct the facility’s first SETI survey.
Rather than requesting new observing time, Mason analyzed data originally collected for other astronomical studies. She searched the observations for narrowband radio signals, which may be more consistent with artificial technology than with naturally occurring cosmic 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 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.”
ALMA Opens a New Frontier for SETI Research
Mason examined two narrow frequency ranges within ALMA’s Band 3 observations. The search did not detect any candidate technosignatures, or potential alien signals, above the survey’s detection thresholds.
The study analyzed only four archived ALMA observations, making it an early and limited investigation. However, the results indicate that telescopes operating at higher radio frequencies could become valuable tools in future searches for extraterrestrial intelligence.
The research also highlights an often-overlooked feature of radio astronomy. When a telescope targets a specific object, its field of view typically includes many additional stars in the surrounding region.
These unintentionally observed stars are sometimes called “stellar bycatch.”
Millions of Stars May Be Hidden in Telescope Data
Astronomers have traditionally estimated the amount of stellar bycatch in an observation using star catalogues such as Gaia. However, catalogues may not include every star within a telescope’s field of view, particularly extremely faint, distant or difficult-to-identify objects.
Instead, Mason used the Besançon Galactic Model, a simulation that estimates the distribution and characteristics of stars throughout the Milky Way. This approach allowed her to calculate the likely number of stars captured in each observation, including stars that are missing from existing catalogues.
When the method was applied to an earlier SETI survey containing 1,327 telescope pointings, the estimated number of stars included in the search increased dramatically. Gaia data identified approximately 288,000 stars, while the galactic model indicated that more than 6.1 million stars may have been observed.
According to Mason, this revised estimate offers a more complete understanding of how much of the Milky Way has already been examined for technosignatures.
“One of the most exciting things about this work is realizing that we’ve surveyed many more stars than initially thought,” she 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.”
No Detected Signal Does Not Rule Out Alien Life
Mason emphasizes that failing to detect a signal does not mean intelligent life does not exist elsewhere. The survey covered only a small number of observations and two limited frequency ranges, and no candidate signal was found within those specific windows.
Instead, the study aims to encourage astronomers to expand SETI surveys across a wider portion of the radio spectrum. It also demonstrates how existing telescope archives can be reused to search for possible signs of extraterrestrial technology without requiring entirely new observing campaigns.
The work was conducted in collaboration with Professor Michael Garrett, Dr. Andrew Siemion and Dr. Kelvin Wandia.
The poster “Strategies Utilising High-Frequency Interferometric Data to Explore SETI Parameter Space” is part of the Statistical Challenges for Next-Generation Astronomical Surveys session at NAM2026.
Source: www.sciencedaily.com