Radio search of K2-18b finds no artificial signals

Astronomers aimed two major radio telescope arrays at K2-18b and found no convincing sign of artificial transmissions, Universe Today reported. The search matters because the planet is considered one of the stronger nearby candidates in the search for life, and the project showed how automated tools can sort through modern SETI data at scale.

The findings were published in The Astronomical Journal in a paper titled “A Narrowband Technosignature Search toward the Hycean Candidate K2-18 b Using the VLA and MeerKAT.” The study used the Karl G. Jansky Very Large Array in New Mexico and the MeerKAT radio telescope in South Africa, an unusual pairing for a single observing campaign, according to Universe Today.

K2-18b sits about 124 light-years from Earth in the constellation Leo, Universe Today reported. It orbits in the habitable zone of a red dwarf star, and James Webb Space Telescope observations have identified carbon dioxide and methane in its atmosphere.

Those observations have made K2-18b a leading candidate for the class of planets known as Hycean worlds, according to Universe Today. In that model, a planet could have a thick hydrogen-rich atmosphere above a global ocean of liquid water.

Millions of signals, no surviving candidate

The researchers searched for narrowband radio signals, the kind of tightly confined transmission often examined in searches for extraterrestrial technology. Universe Today reported that the observations produced millions of possible detections, but none passed all of the screening steps as a credible technosignature.

A major part of the work involved rejecting human-made interference. The VLA data were processed with the Commensal Open Source Multi Mode Interferometer Cluster system, while MeerKAT used the Breakthrough Listen User Supplied Equipment system, according to Universe Today.

The researchers applied five screening methods, the report said. One removed frequencies already known to be contaminated by radio transmissions from Earth, while another used Doppler shifts to reject signals that did not behave as if they were coming from a moving astronomical source.

The team also filtered detections by signal-to-noise ratio, rejecting signals below 10 and above 100, Universe Today reported. The authors noted that this method could have removed some weak extraterrestrial signals, but it also helped cut false detections and instrument artifacts.

Another test used multiple beams from the telescopes. A signal from K2-18b would be expected only in the beam aimed at the planet, while Earth-based interference would tend to appear in more than one beam at the same time, according to the report.

The final planned check would have used the planet’s secondary transit, when K2-18b passed behind its star, to see whether any signal disappeared. Universe Today reported that no such transit occurred during the observations, so that test was not applied.

Limits on possible transmitters

The non-detection still gives astronomers a measurement to work with. Universe Today reported that the study sets upper limits on the strength of any radio transmitter in the K2-18b system, with those limits roughly comparable to the transmitting power of the former Arecibo radar facility in Puerto Rico.

That means the survey did not find a civilization broadcasting with power well above that benchmark in the narrowband frequencies examined, according to Universe Today. It does not rule out life on K2-18b or all possible forms of technology.

The study also tested a workflow for future searches. As facilities such as the Square Kilometer Array begin producing larger data sets, Universe Today reported, automated filtering methods like these will be needed to process the volume of radio signals that SETI surveys collect.

This story draws on original reporting from ScienceDaily.