K2-18b has become one of the most interesting exoplanets in recent years. The planet is located approximately 124 light-years away in the constellation Leo, orbiting within the habitable zone of a red dwarf star. Observations by the James Webb Space Telescope have revealed the presence of an atmosphere rich in carbon dioxide and methane, making K2-18b one of the leading candidates for a “Hycean” world, where a thick hydrogen-rich atmosphere could surround a global ocean of liquid water.
K2-18b is also a prime target for the Search for Extraterrestrial Intelligence (SETI) because of its potential to host conditions favorable to life. Researchers recently used two of the world’s most powerful radio telescopes to search the system for signs of man-made radio transmissions. Their findings were; astronomical journalDespite identifying millions of candidate signals during their observations, they found no evidence of narrowband radio signals comparable to techniques currently used on Earth.
This project combined observations from the Carl G. Janski Very Large Array (VLA) in New Mexico and the MeerKAT radio telescope in South Africa. Coordinating a facility of this size for a single observation campaign is highly unusual and allowed for an extremely sensitive search for the K2-18b system.
Advanced software separates earthly noise from possible alien signals
Gathering observations was only part of the challenge. Equally important are the data processing systems that analyze the vast amounts of radio signals after they are recorded.
Because radio telescopes are constantly bombarded with Earth-generated signals, astronomers rely on sophisticated software to identify and eliminate interference before looking for anything unusual. For this project, VLA used the Commensal open source multimode interferometer cluster system, while MeerKAT relied on the Breakthrough Listen User Supplied Equipment (BLUSE) system. Together, these tools automatically filtered vast amounts of data before researchers performed additional analyses.
The scientists then applied five separate screening methods to search for potential technosignatures.
The first is radio frequency interference (RFI) masking, which removes signals in frequency ranges that are already known to be heavily contaminated by human transmissions. If an extraterrestrial civilization happens to transmit within the same frequency range, detecting it may require a radio telescope somewhere free of Earth’s radio noise, such as the far side of the moon.
How scientists screened millions of candidate signals
The researchers also explained the Doppler effect, the same phenomenon that changes the pitch of passing ambulance sirens. Radio signals traveling between planets should exhibit a measurable Doppler shift as the source and observer move relative to each other. Signals that showed essentially no Doppler changes were almost certainly assumed to originate from Earth and were discarded.
Another filtering step removed signals with signal-to-noise ratios less than 10 or more than 100. This allowed us to eliminate unusually strong instrument artifacts that typically appear on only one antenna, as well as very weak false positives. However, the authors note that this choice may have also excluded some really weak extraterrestrial signals.
The team also performed a multibeam analysis. The telescope produced multiple focused beams simultaneously, one directed at K2-18b and one directed elsewhere in the sky. The real signal from the exoplanet only appears in the beam directed toward K2-18b, but interference from Earth typically appears across multiple beams simultaneously.
The final planned screening method included transit filtering. In principle, the signal emitted by K2-18b should disappear as the planet moves behind its host star. This final test was not necessary, as no such “secondary passes” occurred during the observation activities.
No techno signatures found, but search moved forward
This study yielded millions of potential findings, but none survived all filtering steps. The researchers found no convincing technosignatures within the narrowband radio frequencies they investigated.
The results may seem innocuous, but they provide valuable scientific information. This observation allows astronomers to set an “upper limit” on the strength of radio transmitters that may be present in the K2-18b system. These limits are roughly comparable to the transmission power of the now collapsed Ale Chevy Dar facility in Puerto Rico. Even if a technological civilization exists there, it cannot broadcast anything substantially more powerful than it.
Equally important, this project demonstrated that automated data processing systems can successfully handle the vast number of signals generated during modern SETI observations. Manually inspecting millions of detections is not practical.
As future observatories such as the Square Kilometer Array become operational, these technologies will become even more valuable in processing the unprecedented amount of data being collected. K2-18b may be silent for now, but scientists are steadily improving their ability to detect signs of technology beyond our solar system, should they be heard.
