Dayside magnetodisk reconnection processes on Saturn revealed by Cassini

Magnetic reconnection is a fundamental plasma process that energizes charged particles explosively, generating phenomena such as nebular flares, solar flares, and stunning aurorae. In planetary magnetospheres, magnetic reconnection has often been identified on the dayside magnetopause and in the nightside magnetotail and/or magnetodisk. For giant planets, the dayside magnetodisk is usually considered thicker than the nightside due to the compression of solar wind, and thus not an ideal environment for reconnection. However, in this work, we report a series of evidences of near-noon reconnection within Saturn's magnetodisk using measurements from the Cassini spacecraft. An ion diffusion region is well defined based on the analysis of the Hall magnetic field and the electron pitch angle distribution. The results suggest that the rotationally driven reconnection process plays a key role in producing energetic electrons (up to 100 keV) and ions (several hundreds of kiloelectron volts). In particular, we find that energetic oxygen ions are locally accelerated at the reconnection sites, which shed light to understanding of Jovian X-ray aurorae caused by MeV ion precipitations.