Chinese astronomer studied 33 exoplanetary systems, looking for possible radio signals from alien civilizations. To conduct the observations, they used the FAST (Five Hundred Meter Aperture Spherical Telescope) radio telescope in China, with a reflector distance of 500 meters. Artificial signals may differ from natural signals in narrow frequency bands and many other characteristics. One of the detected signals initially seemed promising to scientists.
Image source: ESO/L. Calcada
Narrowband radio signals are used for communications on Earth, so scientists admit they could also be used by alien civilizations. Natural wireless sources typically emit over a wider range of frequencies. One of the main difficulties in the search is filtering out radio interference caused by our own civilization.
Among the signals recorded during observations of 33 systems, scientists discovered a signal received from the direction of K2-155. The system is 238 light-years away from Earth; previously, an exoplanet was discovered in the star’s potentially habitable zone. The signal at 1140.604 MHz has some characteristics expected from a man-made source: it is narrowband, and its frequency changes due to Doppler shift, as if the source is moving relative to the Earth.
To conduct the test, the scientists used a method of comparing signals in multiple beams (multiple beam coincidence matching). The FAST receiver generates 19 beams that compare signals from a target area of the sky with nearby areas. Signals recorded in multiple beams simultaneously are more likely to represent terrestrial radio interference. The signal in the K2-155 direction was detected in only one beam, thus passing this test.
However, subsequent analysis led scientists to doubt its extraterrestrial origins. In particular, the nature of the polarization raised questions: it was detected in only one channel but not in adjacent channels. This feature is not what researchers expected from a distant artificial transmitter.
The source of this signal, numbered NBS 260108, has not been clearly determined. There is no reason to think it is a message from an alien civilization. At the same time, its research has helped scientists test methods of identifying and filtering radio interference, which will aid further observations.
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