Searching for radio signals finds no sign of an alien civilization on K2-18b

Planet K2-18b, which sparked intense speculation last year due to apparent signs of life, shows no signs of an advanced civilization after a comprehensive search for radio signals from it.

in 2025 Nikku Madhusudhan at the University of Cambridge and his colleagues sensationally claimed that K2-18b, an apparent water world 124 light-years away, shows signs of the molecule dimethyl sulfide (DMS) in its atmosphere. Significant amounts of this molecule only produce life on Earth, so Madhusudhan and his team argued that the signals suggest we may also see signs of life from K2-18b.

However, subsequent observations and more rigorous analyzes showed that the evidence for DMS may instead have come from other molecules not associated with life. Scientists have concluded that the most we can say about a planet is that it is rich in water, either in the form of an ocean or a water-rich atmosphere.

Now Madhusudhan and other researchers have been looking to see if K2-18b might show signs of intelligent life in the form of radio signals emitted into space, like the signals humans have been sending since the 1960s.

They observed K2-18b in several orbits around its star using the Very Large Array telescope in New Mexico and the MeerKAT radio telescope in South Africa, looking for radio signals at similar frequencies to those emitted on Earth. The search would pick up any signals from transmitters of similar strength to Arecibo, the now-defunct radio telescope in Puerto Rico.

But after filtering out potential sources of ground-based interference, they found no signal to suggest that K2-18b has powerful radio transmitters. The researchers declined to speak to him The new scientist about their work.

“If only there was a continuously transmitting Arecibo-class beacon pointed at Earth. [from K2-18b]they would probably find out,” he says Michael Garrett at the University of Manchester in the UK.

“Of course, the non-detection does not tell us that the system is uninhabited. It simply limits a very specific and possibly rare class of signals: persistent, relatively narrow-band radio transmitters operating in the observed frequency range and illuminating the Earth during the observation windows,” says Garrett. “Civilizations, if they exist, may not use radio in this way at all, or may transmit intermittently, directionally, or at much lower power levels. Very low-frequency radio waves may predominate in an aquatic world.”

It’s possible that alien water worlds are suitable for simple life forms, but difficult environments for complex, intelligent life that can develop technology, Garrett says. “Without exposed landmasses, the path to building complex infrastructure could be quite different from what we’ve experienced on Earth.”

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