Searches for radio signals find no hint of alien civilization on K2-18b

The planet K2-18b, which sparked intense speculation last year because of apparent signs of life, shows no signs of advanced civilization after an extensive search for radio signals from it.

In 2025, Nikku Madhusudhan of the University of Cambridge and his colleagues sensationally claimed that K2-18b, an apparently water world 124 light-years away, showed hints in its atmosphere of the molecule dimethyl sulfide (DMS). Significant amounts of this molecule on Earth are only produced by life, so Madhusudhan and his team argued that the signals suggest we may see signs of life from K2-18b as well.

However, subsequent observations and more rigorous analysis showed that the evidence for DMS could instead have come from other molecules not associated with life. Scientists concluded that the most we could say about the 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 looked to see if K2-18b might show signs of intelligent life in the form of radio signals sent out into space, like the signals humans have sent since the 1960s.

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

But after filtering out potential sources of terrestrial interference, they found no signals to suggest that K2-18b had powerful radio transmitters. The researchers declined to speak New Scientist about their work.

“If there was a continuous transmitter, the Arecibo-class beacon aimed at Earth (from K2-18b), they probably would have detected it,” says Michael Garrett of the University of Manchester, UK.

“Of course, a non-detection does not tell us that the system is uninhabited. It simply constrains 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. In a water world, very low-frequency radio waves may be more widespread.”

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

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