A comprehensive search for radio signals from the potentially habitable exoplanet K2-18b has found no evidence of technologically advanced civilizations, though researchers emphasize the finding doesn't rule out other forms of life on the distant world.
The study, conducted using advanced radio telescopes, represents the first coordinated effort to combine SETI (Search for Extraterrestrial Intelligence) observations with recent James Webb Space Telescope detections of potential biosignature gases in K2-18b's atmosphere.
K2-18b, located 124 light-years from Earth in the constellation Leo, has captivated astronomers since JWST detected possible dimethyl sulfide (DMS) in its atmosphere—a gas produced on Earth primarily by biological processes. The sub-Neptune world orbits within its star's habitable zone, where liquid water could exist on the surface.
"We targeted K2-18b precisely because JWST findings made it one of the most promising candidates for life," researchers noted. "The radio survey looked for artificial signals across frequencies commonly used for communication—the kind of emissions a technological civilization would produce."
The observations spanned multiple sessions over several months, listening for narrow-bandwidth signals, broadband emissions, and pulsed transmissions characteristic of artificial sources. The null result means that if intelligent, radio-broadcasting civilizations exist on K2-18b, their signals are either too weak to detect at interstellar distances or operate on frequencies outside the search parameters.
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Critically, the finding does not rule out life itself on K2-18b. "SETI searches for one very specific form of life—technological civilizations that use radio communication," astronomers explained. "K2-18b could harbor microbial life, complex multicellular organisms, or even intelligent species that don't broadcast radio signals."
The research demonstrates how complementary observation strategies create comprehensive pictures of exoplanet habitability. JWST searches for chemical biosignatures—atmospheric compositions inconsistent with purely geological processes. SETI looks for technosignatures—evidence of technology like radio transmissions, optical lasers, or megastructures. Together, they probe different aspects of the life question.
"Earth itself would have been undetectable via SETI for most of its history," researchers noted. "Radio broadcasts have only existed for about 100 years out of 4.5 billion years of life on our planet. We could be looking at a living world that simply hasn't developed radio technology—or developed it long ago and moved on to other communication methods."
The JWST biosignature detections on K2-18b remain tentative and debated within the scientific community. Some researchers question whether the DMS signal truly indicates biological activity or could result from photochemical processes in the planet's hydrogen-rich atmosphere. Follow-up JWST observations are planned to confirm the initial findings.
K2-18b's classification as a "sub-Neptune"—with a radius about 2.6 times Earth's—also complicates habitability assessments. The world likely possesses a thick hydrogen atmosphere and may have a global ocean beneath, but surface conditions remain uncertain. It represents a class of exoplanet unknown in our solar system, where habitability models rely on limited data.
For SETI researchers, the null result adds one more data point to the enduring silence of the cosmos. Despite decades of searching and thousands of known exoplanets, no confirmed technosignature has been detected. This "Fermi Paradox"—the apparent contradiction between high probability of alien civilizations and lack of evidence—continues to puzzle scientists.
Yet the search expands. Next-generation radio telescopes like the Square Kilometer Array will offer unprecedented sensitivity, capable of detecting Earth-strength signals from nearby star systems. Combined with JWST's atmospheric chemistry capabilities, humanity is deploying the most sophisticated alien-hunting tools ever built.
K2-18b remains a priority target for both approaches. The absence of radio signals doesn't diminish its importance—if anything, it highlights the need for patient, multi-wavelength observation of the most promising worlds in our galactic neighborhood.
