A major SETI search found no artificial narrowband radio signal from K2-18b, but it sharpened the tools for future searches.
K2-18b has become one of the most discussed worlds in recent exoplanet research. The planet lies 124 light-years away in the constellation Leo, inside the habitable zone of its red dwarf star.
Observations from the James Webb Space Telescope indicate that its atmosphere contains abundant carbon dioxide and methane. That combination has made it a leading candidate for a “Hycean” world, meaning a planet with a thick hydrogen-rich atmosphere above a global ocean of liquid water.
Because K2-18b is such an appealing target for Search for Extraterrestrial Intelligence (SETI) researchers, scientists used two of the world’s most powerful radio telescopes to monitor its star system. A recent preprint on arXiv reports that, despite millions of possible detections, the team found no likely artificial narrowband radio signals from the planet at a level comparable to current human technology.
Two telescopes joined the search
The observations required both the Karl G. Jansky Very Large Array (VLA) in New Mexico and the MeerKAT radio telescope in South Africa. These rank among the most capable radio telescopes on Earth, and coordinated campaigns between them are highly unusual.
The instruments themselves were only part of the effort. In radio astronomy, the software used to sort and filter incoming data is just as important. Most radio signals detected by these telescopes come from human activity on Earth, so modern searches depend on advanced filtering systems. For this study, the VLA used the Commensal Open-Source Multi-Mode Interferometer Cluster system, while MeerKAT used the Breakthrough Listen User Supplied Equipment (BLUSE) system. Both are essential tools for separating possible astronomical signals from the overwhelming background of terrestrial radio noise.
Earth noise had to be stripped away
The logic of that filtering is still the responsibility of the humans in the loop, though, and the paper describes five different constraints they imposed on the data to screen for potential alien technosignatures. First was RFI masking – essentially they removed all data from signals that fell within frequency bands that were known to be heavily contaminated by terrestrial interference. If the aliens were talking on those channels, we’d have to use some other method – like a radio telescope on the far side of the Moon – to hear them.
Doppler effects, like those that change how an ambulance sounds when it approaches or passes you, are even more prominent when the signal is passing between planets. Any signal with essentially no Doppler change was eliminated outright, as it could only have come from Earth. Perhaps the most debatable logical filtering choice was to eliminate all signals with a signal-to-noise ratio of less than 10 or more than 100. While this eliminated extremely weak false positives, as well as strong instrumental data artifacts typically only seen in one antenna, it could also have eliminated relatively weak actual signals.
Another filtering technique is to use multibeam analysis. In this instance, the telescopes formed coherent “beams” across the sky, with one pointing directly at K2-18b and the other pointing elsewhere. In these cases, a signal coming from the exoplanet would have appeared only in the beam pointed directly at it, while Earth-bound interference bleeds into multiple beams simultaneously. A final check, which wasn’t necessary due to the timing of the survey, is transit filtering. Any signal that appears from K2-18b should go away when the planet passes behind its parent star, but since it didn’t have such a “secondary transit” during the observational window, no such filtering was necessary.
No technosignal survived the filters
In short, despite millions of potential signals throughout the observational window, none passed these filters. There were no definitive technosignatures in the narrowband radio spectrum from K2-18b. While that might sound disappointing, it’s exactly the kind of thing that science needs to advance.
By thoroughly scanning the planet and finding nothing, they are able to place “upper bounds” on the power of a transmitter from that system – in terms of power, it would be something equivalent to the collapsed Arecibo radar in Puerto Rico. If there is a civilization there, they certainly aren’t shouting at us with anything larger than that level of radio telescope.
Perhaps the most important result, though, is the proof of concept for their automated filtering system. Processing the millions of signals the two telescopes discovered by hand would have been next to impossible. So when even larger radio telescopes, like the Square Kilometer Array, come online, these techniques will be ready to help another survey make sense of the mass of data it collects.
While K2-18b might be quiet today, we will continue to get much better at listening if it ever does start to speak to us.
Reference: “A Narrowband Technosignature Search Toward the Hycean Candidate K2-18b Using the VLA and MeerKAT” by C. D. Tremblay, S. Chaudhary, Megan G. Li, Sofia Z. Sheikh, T. Myburgh, D. Czech, D. E. MacMahon, P. B. Demorest, R. A. Donnachie, A. P. V. Siemion, V. Gajjar, M. Lebofsky, K. Wandiak, K. I. Perez and Nikku Madhusudhan, 10 February 2026, arXiv.
DOI: 10.48550/arXiv.2602.09553
Adapted from an article originally published in UniverseToday.
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