SPACE/COSMOS
Could alien signals be hiding on a different radio channel?
image:
ALMA's DV-59 antenna in the foreground with multiple other antennas observing the sky in a night dominated by the Moon.
view moreCredit: ALMA / Alex Pérez / CC BY 4.0
Astronomers searching for signs of extraterrestrial intelligence may have been missing alien signals in part of the radio spectrum that has not recently been explored.
Most radio SETI (Search for Extraterrestrial Intelligence) surveys have focused on frequencies between 1.42 and 1.66 GHz. This range is known as the 'water hole' because it lies between the natural radio frequencies emitted by hydrogen and hydroxyl, two molecules whose combination forms water.
Scientists have long thought that this relatively quiet part of the radio spectrum would be a logical place to communicate, as a technologically advanced civilisation might recognise the significance of hydrogen and hydroxyl and be likely to transmit and listen there.
But a new study suggests that higher radio frequencies could provide an important new avenue in the search for possible technological signals from other civilisations. The research is being presented this week at the Royal Astronomical Society's National Astronomy Meeting in Birmingham.
Using archived observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, astronomer Louisa Mason, a PhD researcher at the University of Manchester, carried out the first-ever SETI survey using the telescope. Rather than making new observations, she analysed existing data originally collected for other astronomical purposes.
She looked for narrowband radio signals that might indicate the presence of 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 searched two small frequency windows in ALMA's Band 3 observations but found no candidate technosignatures (alien signals) above their thresholds.
Although the survey examined only four archived ALMA observations, Mason says the work demonstrates that high-frequency radio telescopes could play an important role in future SETI programmes.
The research also highlights an overlooked opportunity hidden within every radio observation: when astronomers point a telescope at a single target, they also capture many other stars within the telescope's field of view.
Traditionally, researchers have estimated this 'stellar bycatch' using catalogues such as Gaia. Instead, Mason used the Besançon Galactic Model to estimate the full stellar population contained within each observation, including stars too distant, too faint or too difficult to identify reliably in existing catalogues.
Applying the technique to a previous SETI survey of 1,327 telescope pointings increased the estimated number of stars included in the search from around 288,000 identified using Gaia to more than 6.1 million using the galactic model.
Mason says this provides a much more realistic picture of how much of the galaxy has actually been surveyed for technosignatures.
"One of the most exciting things about this work is realising 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."
Mason emphasises that the absence of any detected signal does not mean intelligent life does not exist, only that no candidate signal was found within the small frequency ranges examined in this study. Instead, she hopes the work will encourage future SETI surveys to search more widely across the radio spectrum and make better use of existing astronomical observations.
The work was done in collaboration with Professor Michael Garrett, Dr Andrew Siemion and Dr Kelvin Wandia.
ENDS
Images & captions
Image 1: ALMA's DV-59 antenna in the foreground with multiple other antennas observing the sky in a night dominated by the Moon.
https://drive.google.com/file/d/1qBkjttr8PMnIotJ3m1QM4znBIi7XcGnI/view?usp=drive_link
Credit: ALMA / Alex Pérez / CC BY 4.0
Figure 1: Figure showing the frequency coverage and power of a signal that each facility could be sensitive to. This highlights the fact that no other instruments are conducting SETI at high frequencies, and ALMA has an exciting frequency coverage yet to be explored.
https://drive.google.com/file/d/1B3X3IycbX0bK6GRcQpfP7DPgWWyoUUCg/view?usp=drive_link
Credit: Louisa Mason
Figure 2: Figure of stellar bycatch demonstrating the breadth of stellar objects that could be captured within a single pointing. This example is for a generic direction (l=0 deg, b = 30 deg) for a 5 arc second field of view.
https://drive.google.com/file/d/1FNo5Tupm-PUL_XqBl0PiTxybm235GMA4/view?usp=drive_link
Credit: Louisa Mason
Figure 3: This figure shows the diversity in the stellar bycatch population considered through the use of galactic models (such as BGM). The red overlay is stars found through the Gaia catalogues, highlighting that galactic models simulate the full breadth of Main Sequence stars, as well as clearly distinguishing the white dwarf population.
https://drive.google.com/file/d/16zmO3fq2oeNwmDdz22RrjqUH1Ic-luOf/view?usp=drive_link
Credit: Louisa Mason
Further information
Relevant papers
Louisa A Mason, Michael A Garrett, Andrew P V Siemion, Simulating the stellar bycatch: constraining the prevalence of extraterrestrial transmitters within radio SETI surveys, Monthly Notices of the Royal Astronomical Society, Volume 545, Issue 3, January 2026, staf2112, https://doi.org/10.1093/mnras/staf2112
Louisa A Mason, Michael A Garrett, Kelvin Wandia, Andrew P V Siemion, Conducting high-frequency radio SETI searches using ALMA, Monthly Notices of the Royal Astronomical Society, Volume 536, Issue 3, January 2025, Pages 2127–2134, https://doi.org/10.1093/mnras/stae2714
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 from 14:15-15:45 BST on Friday 24 July 2026 in room PW117. Find out more at: https://uobevents-national-astronomy-meeting-2026.eventsairsite.com/block-schedule.
Notes for editors
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Why Europa’s hidden ocean may be more difficult to reach than scientists thought
A Rutgers scientist says shallow water on Jupiter’s icy moon may not offer a direct window into its deep subsurface
image:
Europa, one of Jupiter’s icy moons, has drawn scientific interest because its frozen surface may hide a global ocean with conditions that could support life.
view moreCredit: NASA/JPL-Caltech/SETI Institute
Europa, one of Jupiter’s icy moons, long has fascinated scientists because of what may lie beneath its frozen shell: a global ocean of liquid water.
That hidden ocean has made Europa one of the most compelling places in the solar system to study the conditions that might support life. But new research led by Rutgers scientist Lujendra Ojha suggests one of the most promising shortcuts to Europa’s ocean may be far more complicated than previously thought.
In a study published in Nature Astronomy, Ojha and colleagues used computer simulations to test whether liquid water from Europa’s deep ocean could rise through cracks in the ice and collect in shallow reservoirs closer to the surface. Such reservoirs, if they exist, could be easier for future missions to detect or sample than the ocean buried far below.
“The mystery we wanted to solve was whether this journey is actually possible,” said Ojha, an associate professor in the Department of Earth and Planetary Sciences at the Rutgers School of Arts and Sciences. “Can liquid water rise from Europa’s deep ocean toward the surface without freezing along the way?”
Their conclusion: The route from deep ocean to shallow ice is probably much more difficult than scientists have assumed.
“There’s an icy shell, there’s water underneath, and there’s all this speculation about how that water can come from deep underground and make its way all the way up without freezing en route,” Ojha said. “That’s really what we think we disproved.”
The finding has important implications for future exploration of Europa. If shallow pockets of liquid water are found beneath the moon’s surface, they may not necessarily contain water from Europa’s deep ocean. Instead, they may have formed locally, from ice that melted within the shell itself.
That distinction matters. Scientists are interested in Europa because liquid water, chemistry and energy are all essential ingredients in the search for habitable environments beyond Earth. A shallow reservoir would be easier to reach than the deep ocean. But if that reservoir isn’t connected to the ocean, it may not reveal what is happening in Europa’s most intriguing environment.
The work arrives as two major spacecraft missions are on their way to the Jupiter system. NASA’s Europa Clipper mission launched in October 2024 and is scheduled to arrive at Jupiter in April 2030, where it will orbit the planet and make 49 close flybys of Europa. The European Space Agency’s Jupiter Icy Moons Explorer mission, known as JUICE, launched in April 2023 and is scheduled to arrive at Jupiter in July 2031.
Together, the missions are expected to give scientists a far more detailed view of Europa’s ice shell, surface composition and possible subsurface water. Europa Clipper’s radar instrument may help scientists determine whether shallow reservoirs exist and how they are structured.
Beneath Europa’s extremely cold surface, a global ocean may remain liquid because Jupiter’s powerful gravity continually squeezes and stretches the moon, generating internal heat that is trapped by the overlying ice shell.
The study focuses on dikes, narrow cracks or fractures that could, in theory, allow water from the ocean to rise upward through the ice. The idea is somewhat similar to the way molten rock can move through cracks on Earth before feeding volcanic activity. On icy worlds, the process is known as cryovolcanism, or volcanism involving ice and water rather than molten rock.
Ojha said that comparison is useful only up to a point.
“Ice and liquid water are fundamentally different than lava and the volcanoes that we see here on Earth,” he said. “I think there’s some fundamental physics that’s missing here, and so I wanted to explore that.”
One missing piece, Ojha said, is turbulence. Earlier models often treated water rising through Europa’s ice as if it moved in a relatively orderly way. But the Rutgers-led simulations suggest the water would likely move fast and turbulently through the fractures, mixing against the cold walls of the crack and losing heat quickly into the surrounding ice.
“This water that’s going to come up, it’s going to be turbulent,” Ojha said. “It’s going to be left and right, it’s going to be up and down, it’s going to have a swirling motion. And when that happens, that liquid water is going to cool very, very fast as it approaches the surface.”
As the water cools, it can become supercooled, meaning it remains liquid even after dropping below its normal freezing temperature. Under those conditions, tiny ice crystals called frazil ice can form, build up and clog the pathway.
The simulations show that narrow cracks could freeze shut within hours. Wider cracks could carry more water under idealized conditions, but turbulence makes those scenarios far less favorable. The researchers found that to deliver enough water to form some of Europa’s surface features, the fractures would need to be unrealistically long or occur in large numbers.
The result is a picture of Europa in which shallow water, if present, may have a different origin than many scientists have hoped. Rather than rising directly from the ocean, the water may be produced by localized heating and melting inside the ice shell.
“Our work suggests that Europa’s ice shell may be a stronger barrier between the ocean and the surface than previously assumed,” Ojha said. “This helps future missions interpret what they find and better understand where to look for signs of habitability.”
Explore more of the ways Rutgers research is shaping the future.
Journal
Nature Astronomy
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Limited direct fluid exchange between the deep subsurface ocean and the shallow subsurface environment of Europa
Article Publication Date
23-Jul-2026
Rocks from unexplored far side of the moon help rewrite lunar history
Ancient samples from the Moon’s far side are helping scientists uncover how asteroid impacts shaped the early Solar System. The findings challenge decades of thinking about when those impacts occurred and offer new insights into the conditions that influenced Earth’s evolution.
Researchers studying lunar rocks have uncovered new evidence about the timing and intensity of asteroid bombardment across the Moon’s surface, finding it declined gradually, rather than being a short, intense burst of impacts as previously thought.
Unlike Earth, where ancient geological evidence has been largely erased by erosion, volcanic activity and shifting tectonic plates, the Moon has preserved a record of impacts stretching back billions of years.
Research co-author Dr Fred Jourdan, from Curtin University’s School of Earth and Planetary Sciences and John de Laeter Centre, said lunar rocks acted as a natural archive of the Solar System’s history, allowing scientists to investigate events that occurred shortly after the planets formed.
“The Moon is like a time capsule — it has preserved a record of events that have been erased from Earth by erosion, plate tectonics and other geological processes,” Dr Jourdan said.
“Samples collected from the Moon’s far side are particularly significant because they allow us to compare two very different parts of the Moon for the first time. Until now, almost everything we knew came from the side facing Earth.”
“By analysing these ancient rocks, we can better understand when major asteroid impacts occurred and how the early Solar System evolved. The far side preserves a cleaner record of those earliest impacts because it was much less affected by later geological events than the side facing Earth.
“These samples are helping us rewrite parts of the Moon’s history and suggest the early Solar System experienced a long decline in asteroid impacts rather than a single catastrophic bombardment.”
The research team analysed tiny fragments of lunar rock, revealing impact events spanning from about 4.33 to 1.13 billion years ago and allowing them to reconstruct more than three billion years of lunar impact history.
Dr Jourdan said understanding the Moon’s impact history could also provide important clues about Earth’s own past.
“The Moon and Earth share a common history, but the evidence of early impacts has largely disappeared from our planet,” Dr Jourdan said.
“Because the Earth and Moon formed together, every major impact recorded on the Moon tells us something about the conditions experienced by the young Earth.
“Studying lunar rocks allows us to look back billions of years and better understand the events that shaped the environments of both worlds and helps us understand the role asteroid impacts played in planetary evolution and the conditions that may have influenced the emergence of life on Earth.
“The findings come amid a new era of lunar exploration and science, with China’s Chang’e-6 mission being the first to return samples from the Moon’s far side.”
The study was led by the State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences.
The paper ‘The bombardment history on the lunar farside revealed by 40Ar/39Ar geochronology of Chang’e-6 impact melt rocks’, is published in Science Advances (doi/10.1126/sciadv.aee8718).
Journal
Science Advances
Method of Research
Content analysis
Subject of Research
Not applicable
Article Title
The bombardment history on the lunar farside revealed by <sup>40</sup>Ar/<sup>39</sup>Ar geochronology of Chang’e-6 impact melt rocks
Article Publication Date
23-Jul-2026
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