Rotationally driven magnetic reconnection in Saturn’s dayside

Guo, R. L., Yao, Z. H., Wei, Y., Ray, L. C., Rae, Jonathan, Arridge, C. S., Coates, A. J., Delamere, P. A., Sergis, N., Kollmann, P., Grodent, D., Dunn, W. R., Waite, J. H., Burch, J. L., Pu, Z. Y., Palmaerts, B. and Dougherty, M. K. (2018) Rotationally driven magnetic reconnection in Saturn’s dayside. Nature Astronomy, 2 (8). pp. 640-645. ISSN 2397-3366

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Abstract

Magnetic reconnection is a key process that explosively accelerates charged particles, 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 magnetodisc, where thin-current-sheet conditions are conducive to reconnection. The dayside magnetodisc is usually considered thicker than the nightside due to the compression of solar wind, and is therefore not an ideal environment for reconnection. In contrast, a recent statistical study of magnetic flux circulation strongly suggests that magnetic reconnection must occur throughout Saturn’s dayside magnetosphere. Additionally, the source of energetic plasma can be present in the noon sector of giant planetary magnetospheres. However, so far, dayside magnetic reconnection has only been identified at the magnetopause. Here, we report direct evidence of near-noon reconnection within Saturn’s magnetodisc using measurements from the Cassini spacecraft. The measured energetic electrons and ions (ranging from tens to hundreds of keV) and the estimated energy flux of ~2.6 mW m–2 within the reconnection region are sufficient to power aurorae. We suggest that dayside magnetodisc reconnection can explain bursty phenomena in the dayside magnetospheres of giant planets, which can potentially advance our understanding of quasi-periodic injections of relativistic electrons and auroral pulsations.

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