First Radio Signals Detected From an Exoplanet

Astronomers using South Africa's MeerKAT telescope detected radio bursts from Beta Pictoris b, the first signal traced directly to an exoplanet.

Astronomers led by Kevin Ortiz Ceballos of the Center for Astrophysics | Harvard & Smithsonian used South Africa's MeerKAT radio telescope array to detect short, repeating bursts of radio waves from Beta Pictoris b, a massive gas giant about 63 to 64 light-years from Earth. It is the first time a radio signal has been unambiguously localized to a single planet rather than its host star.

Multiple outlets were quick to deflate the most exciting-sounding interpretation: this is not a message from an alien civilization. According to Science News, astronomer Yvette Cendes noted that people instinctively think of aliens when they hear 'radio signal from an exoplanet,' but the waves instead likely come from auroras on the planet. As energetic charged particles spiral along the planet's magnetic field lines into its upper atmosphere, they emit circularly polarized radio waves — the same mechanism that powers Jupiter's auroras, which are the strongest auroral radio source in our Solar System.

Previous radio detections from exoplanetary systems could never be traced directly to the planet, because astronomers could not rule out the host star as the source. Two things made this one different. First, the researchers compared their radio images against precisely known positions of distant background quasars, which acted as fixed markers, and the signal lined up with the position of Beta Pictoris b rather than the star. Second, the Live Science reports that Beta Pictoris is an early-type star whose known physical mechanisms cannot produce this kind of radio emission, helping rule it out.

Because auroral emission depends on magnetic field strength, the detection allowed a direct measurement of the planet's magnetism. The team calculated a field of at least 1,250 gauss where the radio waves are produced — vastly stronger than Jupiter's roughly 4.3 gauss and Earth's 0.5 gauss.

Magnetic fields are central to the search for habitable worlds because they shield planetary atmospheres from being stripped away by stellar winds, as Oxford astrophysicist Suzanne Aigrain told Live Science. Earth's magnetic field has played a key role in retaining our atmosphere and shielding life from high-energy radiation. Beta Pictoris b itself is too massive to be a good life candidate, but the technique could eventually be applied to smaller planets where that shielding matters most.

The finding is not yet peer-reviewed, submitted to the arXiv preprint server on September 15, so it must hold up under review — though independent astronomer Joe Callingham of the University of Amsterdam told Science News it would be 'a fantastic result' if confirmed. He notes a clinching test would be seeing the radio pulses rotate in and out of view with the planet's roughly eight-hour spin. Meanwhile, MeerKAT is a pathfinder for the much more powerful Square Kilometre Array, and researchers plan to apply the technique to seven other exoplanets in five star systems.