Astronomers scanning radio data from 33 planetary systems detected a mysterious narrowband signal originating from the direction of K2-155 d, a potentially habitable super-Earth located roughly 238 light-years away, according to findings published in The Astronomical Journal.
A research team led by Zi-Qi Li of Beijing Normal University and Zhengzhou University identified the signal—designated NBS 260108—while re-evaluating older observational data using new machine-learning wavelet analysis software. The data itself was initially captured in 2021 by the Five-hundred-meter Aperture Spherical Radio Telescope, known as FAST, situated in China’s Guizhou Province and operated by the Chinese Academy of Sciences.
Narrow Frequency Structure Reveals Drifting Pattern
The signal quickly drew attention because of its specific frequency structure. Researchers noted that it was concentrated at a narrow band of 1148.4167 megahertz with a signal-to-noise ratio of about 15, packing nearly all its energy into a very thin slice of the radio spectrum.
The signal also exhibited a drifting pattern consistent with an engineered transmitter positioned on a rotating planet orbiting a star, a shift caused by the Doppler effect. Furthermore, the detection appeared to emerge from just one location rather than multiple sources across the sky.
Probing the K2-155 Star System
The target system centers on K2-155, a red dwarf star hosting three super-Earth planets larger than our own. Among them, the outermost planet, K2-155 d, sits within the habitable zone where liquid water could potentially exist under favorable surface conditions.
During the broader survey of 33 planetary systems, the machine-learning pipeline filtered through 139,127 candidate signals. While a separate signal coming from the direction of the star Kepler-438 was quickly identified as equipment-based radio interference, the K2-155 d candidate remained a primary focus of the team’s analysis.
Terrestrial Interference Points to Common Origin
Despite the initial excitement surrounding a potential technosignature, researchers urged caution after discovering that the signal was strong in only one polarization channel of the telescope. Investigators also found similar narrowband features near the same frequency when examining observational data from three other stars—specifically K2-18, GJ-9066, and Ross 128.
These parallel detections strongly favor a common interference origin rather than an artificial transmission originating from K2-155 d. The study’s authors noted that their machine-learning pipeline can generate up to 2.7 million detections under conservative settings, and terrestrial interference can closely mimic narrow, drifting signals coming from a distant exoplanet.