Astronomers have encountered a mystery surprisingly close to Earth. The Guardian and Scientific American have learned that Breakthrough Listen astronomers using the Parkes telescope in Australia discovered a strange radio signal coming from Proxima Centauri, the star system closest to the Sun. The signal occupies an oddly narrow 982MHz band that’s unused by human-made spacecraft, yet not possible through known natural processes. The frequency shifts up, too, rather than down like you’d expect for a planet.Don’t count on this as a sign of aliens. Although Proxima Centauri does host a potentially habitable planet, the signal hasn’t been detected since its initial observation between April and May 2019. Breakthrough Listen said it was still “carefully investigating” and that unusual signals are typically interference researchers couldn’t “fully explain.” As it is, it’s highly unlikely that a radio-capable civilization could live virtually next door without detection — Earth would have been bathed in radio signals from a planet ‘just’ 4.2 light-years away.The most likely explanations so far are either a previously unknown source of Earth-based interference or a newly discovered natural phenomenon.It’s still notable. Signal analysis lead Sofia Sheikh said Breakthrough Listen hadn’t seen a signal pass through “this many of [its] filters” used to catch interference and natural explanations. It’s comparable to the “Wow!” signal from 1977, she said — it’s at least attention-getting. Even though the cause is likely something other than extraterrestrial life, the eventual answer could be very useful.