Preprint claims first direct auroral radio detection and magnetic-field measurement for exoplanet β Pictoris b

A new arXiv preprint claims astronomers have made the first direct detection of auroral radio emission from an exoplanet — and, from that signal, the first direct measurement of an exoplanet’s magnetic field. The reported planet is β Pictoris b, a giant world in a nearby young system, observed with the MeerKAT radio telescope array in South Africa. The findings, posted Sept. 15, are not yet peer reviewed and still need independent confirmation.

If the result holds up, it would fill in a long-missing piece of exoplanet science. Magnetic fields help govern how planets interact with charged particles from their stars and can influence how atmospheres are stripped over time. But while astronomers have inferred magnetic properties indirectly for some exoplanets, they have lacked a direct field-strength measurement.

In the preprint, “Discovery of radio emission from the exoplanet β Pictoris b,” authors K. N. Ortiz Ceballos, Edo Berger and Yvette Cendes of the Center for Astrophysics | Harvard & Smithsonian and the University of Oregon report radio detections from the β Pictoris system in four observing epochs between February 2025 and May 2026. The reported emission spans 0.85 to 3.5 gigahertz and includes rapid, recurring bursts along with fainter steady emission between bursts. The signal is also strongly circularly polarized — a property of radio waves that points to an ordered magnetic process — with reported polarization fractions of about 40% to 70%. The most strongly polarized burst was detected up to 3.5 GHz.

“Here, we report the first direct detection of auroral radio emission from an exoplanet, the giant planet β Pictoris b, with the MeerKAT array,” the authors wrote.

They identify the signal as electron cyclotron maser instability, or ECMI, the same basic auroral radio mechanism seen in planets in our solar system and in some ultracool dwarfs. That matters because ECMI directly traces magnetic field strength: the highest emitted frequency scales with the local magnetic field where the radio waves are produced. Using the 3.5 GHz upper end of the detected emission, the authors infer a magnetic field at the emission site of at least 1.25 kilogauss.

“We identify the emission as electron cyclotron maser radiation, which implies a magnetic field of ≳ 1.25 kG at the planet — the first such direct field strength measurement for an exoplanet,” the paper says.

A central part of the claim is that the radio source can be pinned to the planet rather than the star. After tying the radio images to the Gaia astrometric reference frame, the authors say the source position is consistent with β Pictoris b and inconsistent with the host star at 4.4 sigma and with another known planet in the system, β Pictoris c, at 4.8 sigma. The paper also argues against a stellar origin, saying the host star’s magnetic field is too weak to explain ECMI emission at the observed frequencies and that other proposed drivers are energetically disfavored.

β Pictoris b is already well known to astronomers because it was directly imaged, rather than found indirectly through a transit or a stellar wobble. The preprint lists the β Pictoris system at 19.63 parsecs from Earth. It gives the planet a mass of about 11.9 times Jupiter’s and an orbital distance of about 9.93 astronomical units.

Astronomers have searched for exoplanet radio emission for years, and there have been tentative or disputed claims before. What makes this report stand out is the authors’ argument that they have localized the signal to a known exoplanet rather than to its host star.

For now, though, the result remains a preprint on arXiv, with no peer-reviewed journal publication identified in the research report. The claim that β Pictoris b has produced detectable auroral radio bursts — and that those bursts reveal a directly measured magnetic field — will need review and independent confirmation.