The exoplanet K2-18b, which last year sparked considerable interest due to potential indicators of life, has yielded no evidence of an advanced civilization following an extensive search for radio transmissions.
In 2025, a research team led by Nikku Madhusudhan at the University of Cambridge announced findings suggesting the presence of dimethyl sulphide (DMS) in K2-18b’s atmosphere. This planet, located 124 light-years away, was described as a potential water world. Given that substantial quantities of DMS on Earth are primarily produced by living organisms, Madhusudhan and his colleagues posited that these atmospheric signals might indicate life on K2-18b.
However, subsequent observations and more stringent analyses revealed that the detected evidence for DMS could alternatively originate from non-biological molecules. The scientific consensus shifted, concluding that K2-18b is demonstrably rich in water, either as a surface ocean or within a water-laden atmosphere.
More recently, Madhusudhan and a wider group of researchers turned their attention to detecting signs of intelligent life, specifically through radio signals broadcast into space. This approach mirrors the radio transmissions that humanity has been emitting since the 1960s.
The researchers utilized the Very Large Array telescope in New Mexico and the MeerKAT radio telescope in South Africa to observe K2-18b across several of its orbital periods around its host star. Their objective was to identify radio signals within frequency ranges similar to those used on Earth. The sensitivity of this search was intended to detect any signals emanating from transmitters comparable in strength to the now-decommissioned Arecibo radio telescope in Puerto Rico.
After meticulously filtering out potential sources of terrestrial interference, the team found no signals that would suggest the presence of powerful radio transmitters on K2-18b. The researchers involved have not yet commented publicly on their findings.
Michael Garrett, an astronomer at the University of Manchester, noted that if a continuously transmitting beacon of similar intensity to Arecibo were directed towards Earth from K2-18b, it would likely have been detected. He clarified that a non-detection does not confirm the absence of inhabitants but rather places limits on a very specific type of signal: persistent, relatively narrow-band radio transmissions operating within the observed frequencies and aimed at Earth during the observation windows. Garrett also pointed out that civilizations, should they exist, might employ radio communication differently, perhaps intermittently, directionally, or at much lower power levels. He further suggested that very low-frequency radio waves could be more prevalent on a water world.
Garrett also raised the possibility that alien water worlds might be conducive to simple life forms but present challenges for complex, intelligent life capable of developing technology. He stated that without exposed landmasses, the progression toward building sophisticated infrastructure might diverge significantly from Earth’s developmental path.