Discovery of co-rotating magnetic reconnection in Saturn's magnetosphere

Magnetic reconnection, as a fundamental energy conversion mechanism, can explosively convert energy contained in a magnetic field into ionised particles in solar system, astrophysical plasmas and laboratory plasmas. Planetary magnetic reconnection can be driven by solar wind energy or planetary internal energy. Externally driven processes, from the solar wind, have been extensively investigated at Earth and Mercury. Internally driven processes dictate important dynamics in giant planetary magnetospheres; However, it is not yet established how this process drives magnetospheric energy release and re-loading. Here, using measurements from the Cassini spacecraft in Saturn's magnetosphere, we propose a creative 3D co-rotating reconnection model, which is driven by an internal source. Our results demonstrate that co-rotating magnetic reconnection can drive an expansion of the current sheet in Saturn's magnetosphere, and consequently produce field-aligned electron acceleration. We reveal the nature of 3D reconnection in giant planets, and show the existence of a co-rotating reconnection process in the universe. Our co-rotating reconnection picture can be widely applied to the fast rotating magnetised plasma environments in the solar system and beyond. For example, magnetic reconnection is a potential heating source for the interstellar medium and halo gas.