Astronomers have conducted a thorough search for radio signals from the exoplanet K2-18b, a potential water world 124 light years away, but detected none indicative of advanced life. The planet previously sparked interest due to possible atmospheric signs of life, though those claims were later questioned. This latest effort used powerful telescopes to scan for transmissions similar to Earth's.
The exoplanet K2-18b, located 124 light years from Earth, has long intrigued scientists as a possible water-rich world. In 2025, Nikku Madhusudhan at the University of Cambridge and his team reported hints of dimethyl sulphide (DMS) in its atmosphere, a molecule primarily produced by living organisms on Earth. This led to speculation about biological activity on the planet.
However, follow-up studies suggested the DMS signals might stem from non-biological molecules instead. Researchers now describe K2-18b as rich in water, possibly featuring an ocean or a water-vapor-dominated atmosphere.
Building on this, Madhusudhan and colleagues turned to the search for technological signs of life. They observed K2-18b over multiple orbits of its star using the Very Large Array telescope in New Mexico and the MeerKAT radio telescope in South Africa. The team targeted radio frequencies akin to those humans have broadcast since the 1960s, aiming to detect signals from transmitters as powerful as the former Arecibo observatory in Puerto Rico.
After accounting for Earth-based interference, no such signals were found. The researchers did not comment on their findings to New Scientist.
Michael Garrett at the University of Manchester, UK, noted the implications: “If there were a continuously transmitting, Arecibo-class beacon directed toward Earth [from K2-18b], they likely would have detected it.” He added that the absence of detection limits possibilities for certain types of signals, such as persistent, narrow-band radio emissions in the scanned range. Civilizations might avoid such broadcasts, opting for intermittent, directional, or lower-power methods. On a water world like K2-18b, low-frequency radio could dominate instead.
Garrett also suggested that water worlds may support simple life but pose challenges for developing complex, technology-building societies without land surfaces, potentially altering evolutionary paths from Earth's experience.
The study is detailed in a preprint on arXiv (DOI: 2602.09553).