Beta Pictoris b Field Measured at 1,250 Gauss, Tops Jupiter

Astronomers say the auroral radio bursts from Beta Pictoris b yield the first direct measurement of an exoplanet's magnetic field, around 1,250 gauss.

The headline detection from MeerKAT was the radio bursts themselves, but the new development underneath is the measurement they enable. Using the auroral emissions from Beta Pictoris b, a team led by Kevin Ortiz Ceballos at the Center for Astrophysics, Harvard & Smithsonian calculated a magnetic field strength of at least 1,250 gauss where the radio waves are produced — the first direct measurement of magnetic field strength for any exoplanet. Co-author Yvette Cendes of the University of Oregon told Science News, per starlust.org, that it is 'an incredibly, incredibly strong magnetic field, much stronger than anything in our solar system.'

Both outlets report the field in the radio-emitting region is far stronger than Jupiter's, and starlust.org adds that Earth's own field is only about half a gauss. The strength is less shocking when the planet's size is considered: starlust.org reports Beta Pictoris b is roughly ten times Jupiter's mass, putting it closer to brown dwarfs, which show auroral evidence of fields in the thousands of gauss. The team notes the result matches theoretical predictions for young, massive giant planets, suggesting it is not an anomaly and giving theorists a real number to test their models of planetary interiors against.

The key evidence that made a measurement possible was source localization. Earlier exoplanet radio hunts kept failing because nobody could tell whether emission came from the star or a planet. The team solved this by comparing their radio images with the precise positions of extremely distant background quasars, which served as fixed markers on the sky. Layering the radio images over that quasar-anchored map showed the bursts lined up with Beta Pictoris b's position, not its parent star's. Supporting the auroral interpretation, starlust.org reports the signals were circularly polarized, the hallmark of auroral radio emission.

Neither outlet suggests anything extraterrestrial: the bursts are auroras, produced as charged particles spiral along magnetic field lines into the upper atmosphere, the same mechanism behind Earth's northern lights. The stakes are scientific rather than speculative — magnetic fields shape how radiation and stellar wind strip planetary atmospheres, so a direct field measurement offers a new probe of what giant exoplanets are like inside. The paper has been posted to arXiv but is not yet peer-reviewed, so confirmation through publication is the next step, with more young giants likely candidates for the same MeerKAT technique.