BY:SpaceEyeNews.
Astronomers have completed an unusually powerful K2-18b alien signal search, using two major radio telescope arrays to investigate whether the distant planetary system contains detectable technology.
The campaign produced millions of potential radio detections. However, none survived the team’s full screening process. Researchers found no convincing narrowband signal linked to an artificial transmitter near K2-18b.
That result does not prove that the planet is lifeless. It also does not rule out a technological civilization. Instead, the survey tested a specific possibility: whether the system contains a persistent and sufficiently powerful radio transmitter within the observed frequencies.
The most important result may therefore be the search method itself. By combining multiple telescopes, observing periods and automated filters, the researchers created a framework that could improve future searches for technology beyond Earth.
Why K2-18b Became a Major SETI Target
K2-18b lies about 124 light-years away in the constellation Leo. It orbits a cool red dwarf star and completes one orbit in roughly 33 days.
The planet has attracted intense attention because it sits within its star’s habitable zone. However, K2-18b is not an Earth-like world. Scientists classify it as a sub-Neptune, with a radius about 2.6 times larger than Earth’s and a mass roughly 8.6 times greater.
James Webb Space Telescope observations have confirmed methane and carbon dioxide in its atmosphere. These findings led some scientists to suggest that K2-18b could be a Hycean-world candidate.
A Hycean planet may contain a hydrogen-rich atmosphere above a deep global ocean. Such conditions could potentially support chemistry related to life. Yet scientists have not confirmed that K2-18b has an ocean, a habitable surface or any biological activity.
Claims involving possible biosignature gases have also remained controversial. Independent analyses have argued that current data do not meet the standards needed to claim evidence of life.
Even so, the planet remains an attractive target. Atmospheric studies search for signs of biological chemistry. SETI investigations ask a different question: could technology around the planet produce a signal that Earth-based instruments can detect?
K2-18b Alien Signal Search Used Two Telescope Arrays
For the new campaign, researchers combined observations from the Karl G. Jansky Very Large Array in New Mexico and the MeerKAT radio telescope in South Africa.
The Very Large Array, commonly called the VLA, consists of 27 radio antennas. Scientists can combine their signals to operate the facility as one highly sensitive instrument.
MeerKAT contains 64 radio dishes in South Africa’s Northern Cape. It also serves as an important precursor to the Square Kilometre Array, a much larger international radio observatory under development.
Using both facilities gave the researchers broader frequency coverage and several independent observing periods. The campaign examined frequencies between 544 megahertz and 9.8 gigahertz.
MeerKAT collected observations in several bands during September and October 2023. The combined VLA and MeerKAT data covered multiple epochs and at least one complete orbit of K2-18b.
This approach offered a major advantage. A single short observation might miss an intermittent signal. Repeated observations can reveal whether a candidate returns, changes with the planet’s motion or appears only during a specific orbital phase.
The project also used separate computing systems at each telescope. The VLA relied on the Commensal Open Source Multimode Interferometer Cluster, known as COSMIC. MeerKAT used the Breakthrough Listen User Supplied Equipment system, or BLUSE.
Both systems can process large amounts of radio data while the telescopes perform other scientific work.
What Kind of Alien Signal Did Scientists Seek?
The team focused on narrowband radio emissions.
A narrowband signal concentrates most of its energy inside a very small frequency range. Many natural astronomical objects produce radio waves across wider sections of the spectrum.
Human technologies, by contrast, often generate narrowband transmissions. Radio communication systems, radar installations and spacecraft links can all create signals that occupy tightly defined frequencies.
For that reason, SETI researchers often treat unusual narrowband signals as possible technosignatures. A technosignature is evidence that could point to technology rather than biology.
Still, detecting a narrow signal does not automatically make it extraterrestrial. Earth produces an enormous amount of radio interference. Satellites, aircraft, mobile networks, navigation systems and electronic equipment can all appear inside astronomical observations.
The central challenge was not finding signals. The telescopes found millions. The difficult task was proving that any signal came from the direction of K2-18 rather than from Earth.
Search for radio signals finds no hint of alien civilisation on K2-18b.
How Scientists Filtered Millions of Radio Signals
The research team developed a multi-stage screening process. Each stage removed candidates that showed characteristics associated with human interference or telescope artifacts.
Known Interference Frequencies Were Masked
First, researchers removed frequencies known to contain heavy radio frequency interference.
Many parts of the radio spectrum carry regular signals from Earth-based communication systems and satellites. These contaminated regions can produce thousands of false candidates.
Masking them greatly reduces the amount of data that researchers must inspect. However, it creates a limitation. An extraterrestrial civilization might use the same frequencies.
A signal hidden inside a heavily contaminated band could remain undetectable from Earth. Future searches from radio-quiet locations, such as the far side of the Moon, could avoid some of this interference.
Doppler Drift Helped Identify Local Signals
The team also examined how candidate frequencies changed over time.
Movement between a transmitter and receiver causes a Doppler shift. It is similar to the change in pitch heard when a siren passes an observer.
Earth rotates and orbits the Sun. K2-18b also moves around its host star. A signal traveling between the two systems should therefore drift in frequency at a measurable rate.
A signal with little or no expected drift was more likely to come from a local source. Researchers used the known motion of the K2-18 system to define which drift rates appeared physically plausible.
This step removed large numbers of stationary or nearly stationary detections.
Multiple Beams Separated Space Signals From Earthly Noise
Multibeam analysis provided another powerful test.
The telescopes formed several focused listening beams. One beam pointed toward K2-18, while other beams monitored different positions in the sky.
A real signal associated with the target system should appear mainly in the beam aimed at K2-18. Local interference often enters several beams at once.
When the same detection appeared across multiple beams, researchers classified it as likely human-made interference.
This spatial comparison helped eliminate signals that might otherwise have looked promising when viewed in only one data stream.
Signal Strength Filters Removed False Detections
The researchers also screened candidates using their signal-to-noise ratios.
Signals with a ratio below 10 were considered too weak to classify reliably. Random noise can easily create apparent detections at low values.
The team also removed candidates with ratios above 100 in parts of the analysis. Extremely strong signals that appear in only one antenna often come from instrumental effects rather than distant transmitters.
This filter created another trade-off. A genuinely faint extraterrestrial signal could fall below the selected threshold. Scientists therefore cannot claim that the search excluded every possible transmission.
What the K2-18b Alien Signal Search Found
After applying all screening methods, no candidate remained consistent with an artificial or astrophysical narrowband source from the K2-18 system.
The researchers placed limits on persistent, isotropic transmitters with effective powers between approximately 10¹² and 10¹³ watts. The precise limit varied across the observing bands.
An isotropic transmitter sends energy in every direction. This is an inefficient way to communicate across interstellar distances, but it gives scientists a standard model for comparing searches.
The limits are broadly comparable to the effective power of Earth’s former Arecibo planetary radar. Arecibo could produce an extremely powerful, focused radio beam for studying planets and asteroids.
However, that comparison requires caution. A civilization might use a tightly directed beam rather than broadcast in every direction. Earth would only detect that signal if the beam crossed our position during the observations.
The nondetection therefore means that researchers found no persistent transmitter above their sensitivity limits in the frequencies they searched. It does not mean that the entire system is radio silent.
What the Nondetection Does Not Rule Out
A technological civilization could remain undetected for many reasons.
It might use frequencies outside the surveyed range. Its transmitter could operate below the telescopes’ sensitivity limits. It could also send short, intermittent messages that did not occur during the observing windows.
Directional communication creates another challenge. A civilization may aim narrow beams at nearby planets, spacecraft or other stars. Unless one of those beams points toward Earth, our telescopes would hear nothing.
Alien technology might also use communication methods that researchers are not currently searching for. Optical lasers, infrared emissions, unusual atmospheric chemicals or large artificial structures could all produce different technosignatures.
Furthermore, K2-18b itself may not offer suitable conditions for life. A thick hydrogen atmosphere could create extreme pressures and temperatures deeper inside the planet. Some models suggest it may lack an accessible liquid-water ocean.
The K2-18b alien signal search tested one narrow technological scenario. It did not deliver a final judgment on the planet’s habitability or its potential to host life.
Why This Search Still Represents Progress
Negative results matter when researchers can measure what their instruments would have detected.
The new study established clear upper limits on certain radio transmitters. Future surveys can improve those limits or search different frequency ranges.
More importantly, the campaign demonstrated how automated systems can process millions of candidate signals. Manual inspection would have taken too much time and could have produced inconsistent decisions.
The framework combined known interference masks, Doppler analysis, multibeam comparisons and signal-strength filtering. Researchers can now adapt this process for other potentially habitable planets.
Coordinated observations also improve confidence. When separate facilities observe the same system, scientists gain more opportunities to reject local interference.
Future observatories will make this capability essential. The Square Kilometre Array will collect enormous volumes of radio data. Its sensitivity could reveal much weaker signals than current instruments can detect.
Yet greater sensitivity will also reveal more interference and more false positives. Advanced filtering systems must therefore improve alongside telescope hardware.
K2-18b Remains Interesting, but the Evidence Requires Caution
K2-18b continues to occupy an unusual position in exoplanet research.
Its atmosphere contains confirmed carbon-bearing molecules. Its size and temperature make it easier to study than smaller Earth-sized planets. At the same time, scientists continue to debate its internal structure and potential habitability.
The new radio survey adds another layer to that investigation. It found no evidence of technology, but it created the first interferometric technosignature constraints aimed specifically at a Hycean-planet candidate.
Scientists should not describe the result as proof that aliens do not exist on K2-18b. Nor should they interpret previous atmospheric findings as proof that life exists there.
Both claims would go beyond the available evidence.
Conclusion
The K2-18b alien signal search found no convincing artificial radio transmissions. Millions of initial detections disappeared after researchers removed Earth-based interference, instrumental artifacts and signals with implausible motion.
Yet the survey delivered a meaningful scientific result. It showed that coordinated radio observatories can examine a promising exoplanet across several frequencies and observing periods while processing vast amounts of data automatically.
K2-18b has not revealed evidence of a technological civilization. However, astronomers now have a stronger method for detecting one.
For now, the planet remains quiet within the limits of this search. The wider message is more encouraging: scientists are becoming much better at recognizing a genuine signal if one eventually reaches Earth.
Main Sources:
A Narrowband Technosignature Search Toward the Hycean Candidate K2-18b Using the VLA and MeerKAT
https://arxiv.org/abs/2602.09553
Full study text and methodology
https://arxiv.org/html/2602.09553v1
ScienceDaily coverage
https://www.sciencedaily.com/releases/2026/07/260712011748.htm
K2-18b Does Not Meet the Standards of Evidence for Life
https://arxiv.org/abs/2508.05961