A search for radio signals from the exoplanet K2-18b has returned nothing — no transmissions, no beacons, no evidence of any technologically advanced civilization broadcasting into space.
K2-18b is a planet 124 light years from Earth that generated considerable scientific attention in 2025 when a team led by Nikku Madhusudhan at the University of Cambridge reported atmospheric hints of dimethyl sulphide, a molecule that on Earth is produced almost exclusively by living organisms. The claim was measured but provocative: this might be a sign of life on another world. Subsequent observations, however, complicated that picture. More rigorous analysis revealed that the spectral signal attributed to dimethyl sulphide could have originated from other molecules with no biological connection. The strongest conclusion researchers could draw was that K2-18b is rich in water — either hosting an ocean or a water-saturated atmosphere.
Now Madhusudhan and colleagues have taken a different approach to the same question. Rather than searching for biosignatures in the planet’s chemistry, they searched for technosignatures — specifically, radio signals of the kind that intelligent, technologically capable civilizations might emit. Humans have been broadcasting such signals since the 1960s. The logic is straightforward: if something similar were happening on K2-18b, a sufficiently sensitive telescope might pick it up.
The team used two of the world’s most capable radio observatories — the Very Large Array in New Mexico and the MeerKAT telescope in South Africa — to monitor K2-18b across several orbits around its host star. They focused on frequency ranges comparable to those used in terrestrial broadcasting. The sensitivity was sufficient to detect any transmitter with power roughly equivalent to Arecibo, the large but now-demolished radio telescope in Puerto Rico. After removing terrestrial interference from the data, they found nothing.
Michael Garrett at the University of Manchester offered useful context for what that absence actually means. A continuously transmitting Arecibo-equivalent beacon aimed at Earth would likely have been detected, he said. But the absence of a detection doesn’t mean the planet is uninhabited. It constrains one specific class of signals: persistent, narrowband transmissions operating in the observed frequency range and pointing toward Earth during the observation windows. Any civilization that transmits intermittently, directionally, at lower power, or at frequencies outside the observed range would not have been caught.
Garrett raised another possibility worth considering. On a water world with no exposed landmasses, the development of complex, technology-building civilization might follow an entirely different trajectory — or face obstacles that simply don’t exist on a planet like Earth. Infrastructure requires land. The engineering pathways that allowed humans to build radio transmitters depended on geology, on accessible materials, on environments where certain kinds of complexity could take hold. An ocean world might be hospitable to simple life and still be a difficult place for anything more sophisticated to emerge.
That distinction — between life and intelligent, communicating life — is easy to collapse in popular discussion. This search was always targeting the narrow end of a very wide possibility space.
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