Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
EPSC Abstracts
Vol. 14, EPSC2020-213, 2020, updated on 11 Dec 2023
https://doi.org/10.5194/epsc2020-213
Europlanet Science Congress 2020
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Saturn’s nightside ring current during Cassini’s Grand Finale

Gabrielle Provan1, Tom Bradley1, Emma Bunce1, Greg Hunt2, Stan Cowley1, Hao Cao3,4, Michele Dougherty2, Elias Roussos5, and Chihiro Tao6
Gabrielle Provan et al.
  • 1School of Physics and Astronomy, University of Leicester, Leicester, UK (gp31@le.ac.uk)
  • 2Blackett Laboratory, Imperial College London, London, UK
  • 3Department of Earth and Planetary Sciences, Harvard University, USA
  • 4Division of Geological and Planetary Sciences, California Institute of Technology, CA 91125, USA
  • 5Max Planck Institute for Solar System Research, Göttingen, Germany
  • 6National Institute of Information and Communications Technology, Koganei, Japan

During Cassini’s Grand Finale proximal orbits, the spacecraft traversed the nightside magnetotail to ~21 Saturn radii.  Clear signatures of Saturn’s equatorial current sheet are observed in the magnetic field data.  An axisymmetric model of the ring current is fitted to these data, amended to taken into account the tilt of the current layer by solar wind forcing, its teardrop-shaped nature and the magnetotail and magnetopause fringing fields.  Variations in ring current parameters are examined in relation to external driving of the magnetosphere by the solar wind, and internal driving by the two planetary period oscillations (PPOs) and compared with dawn and dayside regimes.  The relative phasing of the PPOs determines the ring current’s response to solar wind conditions. During solar wind compressions when the PPOS are in antiphase, magnetospheric storms are triggered and a thick partial ring current is formed on the nightside, dominated by hot plasma injected by tail reconnection.  However, during solar wind compressions when the PPOs are in phase, the magnetosphere shows only a ‘minor’ response and a partial ring current is not observed. During solar wind rarefactions an equatorial ‘magnetodisc’ configuration is observed in the dayside/dawn/nightside regions, with similar total currents flowing at these local times.  This partial ring current should close partly via magnetopause currents and possibly via field-aligned currents into the ionosphere.  During very quiet intervals of prolonged solar wind rarefaction, a thin current sheet with an enhanced current density is formed, indicative of a ring current dominated by cool, dense, Enceladus water group ions.

How to cite: Provan, G., Bradley, T., Bunce, E., Hunt, G., Cowley, S., Cao, H., Dougherty, M., Roussos, E., and Tao, C.: Saturn’s nightside ring current during Cassini’s Grand Finale , Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-213, https://doi.org/10.5194/epsc2020-213, 2020.