Overview
Astronomers have identified an unusual radio signal associated with the direction of K2-155, a red-dwarf star system approximately 238 light-years from Earth. The signal, detected in archival observations from China’s Five-hundred-meter Aperture Spherical Telescope (FAST), has attracted attention because of several characteristics sometimes considered important in the search for technological activity.
However, the finding is not evidence of extraterrestrial life or an alien transmission. The signal’s origin remains unresolved, and the available data leave open the possibility that it was produced by radio interference on Earth, an instrumental effect or another natural phenomenon. The results were reported in The Astronomical Journal.
A signal with unusual characteristics
The signal has been designated NBS 260108 and was recorded at a frequency of 1,148.4167 megahertz. Researchers said it was exceptionally narrow in frequency and appeared to drift over time. Such frequency movement can occur naturally, but it can also resemble the changes expected from a transmission originating on a rotating and orbiting planet.
FAST’s observing system provided another initially intriguing detail. The telescope uses 19 separate receiver beams to survey the sky. NBS 260108 appeared in the beam aimed toward K2-155 and was not detected in the other 18 nearby beams. A signal confined to one beam can be consistent with a distant astronomical source, although it does not by itself establish that the signal came from the target system.
The signal emerged from a new analysis of older FAST observations covering 33 planetary systems. Researchers used machine-learning tools and wavelet analysis to sift through a large volume of radio data. The initial process identified more than 139,000 potential detections, which were narrowed through successive rounds of filtering. Two signals remained especially noteworthy: one was linked to human-generated interference, while NBS 260108 remained unexplained.
Why K2-155 attracted interest
K2-155 is known to host three planets, including K2-155d, a super-Earth estimated to be about 1.6 times Earth’s radius. The planet orbits near the star’s habitable zone, the region where temperatures could, under suitable atmospheric conditions, permit liquid water to exist on the surface.
That location makes K2-155d an appealing target for astronomical study, but being in or near the habitable zone does not mean a planet is inhabited. Scientists would need evidence about its atmosphere, surface conditions and long-term climate before assessing whether it could support life. A radio signal alone, particularly one detected only once, cannot answer those questions.
Significant caveats remain
The researchers also found reasons to suspect that NBS 260108 may not have originated near K2-155. Similar signals appeared at nearby frequencies while FAST was observing three other stars, and the unusual detection was substantially stronger in only one polarization channel. Those patterns can be associated with terrestrial interference or telescope-related effects.
For now, the signal is best described as unexplained rather than extraterrestrial. Additional observations of K2-155, ideally using independent telescopes and instruments, could determine whether the signal repeats, follows the expected motion of the planetary system or can be traced to a local source. Until such tests are completed, the discovery represents a useful target for follow-up research—and a reminder that unusual signals require careful verification before they can be interpreted as possible technosignatures.
