Discovery of radio emission from the exoplanet $\beta$ Pictoris b

Planetary magnetic fields shape atmospheric escape, mediate interactions with stellar winds, and encode information about planetary interiors, yet they have not been directly measured for planets beyond the Solar System. A direct observable signature is auroral radio emission produced by the electron cyclotron maser instability, whose highest emitted frequency is set by the magnetic field strength at its source. Although auroral radio bursts are observed in Solar System planets and in some ultracool dwarfs, no radio detection had previously been unambiguously localized to an extrasolar planet rather than its host star.

Here, researchers report the first direct detection of auroral radio emission from an exoplanet, the giant planet β Pictoris b, using the MeerKAT array. They detect rapid, recurring, and highly circularly polarized bursts, as well as persistent emission, at frequencies of 0.85 to 3.5 GHz.

The emission is identified as electron cyclotron maser radiation, which implies a magnetic field of ≳1.25 kG at the planet. This is the first direct magnetic field strength measurement for an exoplanet, opening a new way to probe planetary magnetism and its role in atmospheric escape and star-planet interactions.