SETI researchers used the VLA and MeerKAT telescope to search for narrow radio signals from the intriguing exoplanet. None survived the noise filters, but the method will be used in future searches
K2-18b has become one of the most talked-about worlds in exoplanet research recently. It lies 124 light-years away in the constellation Leo, within the habitable zone of a red dwarf.
Observations from the James Webb Space Telescope indicate that its atmosphere contains abundant carbon dioxide and methane. This combination makes it a leading candidate for being a "Mimenus" world, a planet with a dense, hydrogen-rich atmosphere above a global ocean of liquid water.
Because K2-18b is such an attractive target for SETI researchers, scientists used two of the world's most powerful radio telescopes to track its star system. In a preprint on the arXiv website, they report that despite millions of potential detections, the team found no potential artificial narrowband radio signals from the planet at a level comparable to existing human technology.
Two telescopes joined the search
The observations used the Very Large Array (VLA) in New Mexico and the MeerKAT radio telescope in South Africa. Both are among the most powerful radio telescopes on Earth, and their coordinated observation systems are very unusual.
The instruments themselves were only part of the operation. In radio astronomy, the software used to sort and filter the data received is just as important. Most of the radio signals these telescopes pick up come from human activity on Earth, so modern searches depend on sophisticated filtering systems. The software is a vital tool for separating possible astronomical signals from the vast background noise of terrestrial radio signals.
The earthly noise had to be removed.
The logic of this filtering is still up to the humans involved, and the paper describes five different constraints that were imposed on the data to filter out possible alien technological signatures. The first was RFI masking – they essentially removed all data from signals that were in frequency ranges known to be heavily contaminated with terrestrial interference. If aliens were speaking on these channels, we would have to use another method – like a radio telescope on the far side of the moon – to hear them.
Doppler effects, such as those that change how an ambulance sounds as it approaches or passes us, are even more pronounced when the signal travels between planets. Any signal without a Doppler shift is immediately discarded, because it could only have come from Earth. The most controversial logical filtering choice was to discard all signals with a signal-to-noise ratio of less than ten or more than one hundred. This filtering eliminated very weak false positives, as well as strong data from instrumentation that is usually observed with only one antenna, but it could also discard relatively weak real signals.
Another filtering technique is the use of multibeam analysis. In this case, the telescopes created coherent “beams” in the sky, with one pointed directly at K2-18b and the other pointed elsewhere. In these cases, a signal from the exoplanet would only appear in the beam pointed directly at it, while interference from Earth would spill over into multiple beams at once. A final check, which was not necessary due to the timing of the survey, is transit filtering. Any signal from K2-18b should disappear when the planet passes behind its host star, but since no such “secondary transit” occurred during the observation window, this type of filtering was not necessary.
No technological signal passed the filters.
In short, despite millions of potential signals during the observation window, not a single signal passed these filters. There were no definitive technological signatures in the narrow range of radio frequencies.
From K2-18b. It may sound disappointing, but these are exactly the kinds of things science should promote.
They have thoroughly surveyed the planet and found nothing, which allows them to place “upper bounds” on the power of a transmitter from this system – in terms of power, it would be equivalent to the Arecibo radar in Puerto Rico that crashed. If there is a civilization there, they are certainly not shouting at us with anything larger than a radio telescope of this caliber.
But perhaps the most important result is the proof of concept of the automatic filtering system, which will be ready for use when larger radio telescopes are put into operation.
Short FAQ:
Have alien signals been found from K2-18b?
No. The scan did not find any narrow radio signals that passed the noise filters and could be considered a possible technological signature.
Why is K2-18b so interesting to researchers?
It is located in the habitable zone of a red dwarf, and observations from the James Webb Space Telescope have indicated atmospheric components that raise interest in the possibility of a hydrogen-rich world and perhaps an ocean.
What were the researchers actually looking for?
They looked for radio signals in a narrow frequency range, the kind considered a possible candidate for an artificial technological signature.
Why is a negative result still important?
It allows for setting upper limits on the strength of a possible transmitter in the system, and especially for testing and improving filtering methods that will be used in future searches.
More of the topic in Hayadan:
One response
Even if there is life there, who said it was technological? I think the humans on this planet really broke conventions. And beyond that, who said they were smart like humans and not stupid like dinosaurs?