A rapidly time-varying equatorial jet in Jupiter's deep interior

Planetary magnetic fields provide a window into the otherwise largely inaccessible dynamics of a planet's deep interior. Interaction between fluid flow in electrically conducting regions and the magnetic field produces observable secular variation of the external field. Recent observations revealed secular variation of Jupiter’s field, partly arising from an axisymmetric equatorial jet. Whether this jet is time dependent had not been addressed, yet is critical for understanding interior dynamics: a steady jet would likely reflect deep dynamo convection, whereas time dependence on a timescale much shorter than the convective turnover time (hundreds of years) would imply a different origin. Here we show that Jupiter’s equatorial jet exhibits a wavelike fluctuation with a period of roughly 4 years, indicative of a torsional oscillation or a localized Alfvén wave in the metallic hydrogen interior. This finding opens a pathway to probing otherwise hidden aspects of the interior magnetic field and constraining the dynamo that generates Jupiter’s magnetic field.