Saturn's near-equatorial ionospheric conductivities from in situ measurements

Creators: Shebanits, O.; Hadid, L. Z.; Cao, H.; Morooka, M. W.; Hunt, G. J.; Dougherty, M. K.; Wahlund, J.-E.; Waite, J. H., Jr.; Müller-Wodarg, I.

Abstract

Cassini's Grand Finale orbits provided for the first time in-situ measurements of Saturn's topside ionosphere. We present the Pedersen and Hall conductivities of the top near-equatorial dayside ionosphere, derived from the in-situ measurements by the Cassini Radio and Wave Plasma Science Langmuir Probe, the Ion and Neutral Mass Spectrometer and the fluxgate magnetometer. The Pedersen and Hall conductivities are constrained to at least 10⁻⁵–10⁻⁴ S/m at (or close to) the ionospheric peak, a factor 10–100 higher than estimated previously. We show that this is due to the presence of dusty plasma in the near-equatorial ionosphere. We also show the conductive ionospheric region to be extensive, with thickness of 300–800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities from orbit 288 to 292.

Additional Information

© The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received 20 December 2019; Accepted 21 April 2020; Published 13 May 2020. All the data included in the present study and shown in the figures is publicly available in the NASA Planetary Data System archive. Work at Imperial College London was funded by Science and Technology Facilities Council (STFC) consolidated grant ST/N000692/1. The RPWS/LP instrument on board Cassini is supported by the Swedish National Space Agency (SNSA). O.S. acknowledges funding by the Royal Society grant RP\EA\180014. L.Z.H. acknowledges funding by the Swedish Research Council (Vetenskapsrådet, VR) under contract 2016-05364. H.C. acknowledges funding by NASA's CDAPS program NNX15AL11G and NASA Jet Propulsion Laboratory (JPL) contract 1579625. H.C. also acknowledges Royal Society Grant RP\EA\180014 to enable an academic visit to Imperial College London, during which some of the work has been carried out. M.W.M. acknowledges funding by the SNSA under contract Dnr 174/15. G.J.H. acknowledges funding by STFC Consolidated grant ST/N000692/1. M.K.D. acknowledges funding by Royal Society Research Professorship RP140004. J.H.W. acknowledges funding by NASA JPL subcontract (NASA contract NAS703001TONMO711123, JPL subcontract 1405853). Author Contributions: O.S., M.K.D., J.E.W. G.J.H. and H.C. designed the study. O.S. carried out the primary analysis and had the main responsibility for writing the manuscript. L.Z.H. contributed with initial analysis. H.C. processed the MAG dataset. M.W.M. processed the RPWS/LP dataset. J.H.W. processed the INMS dataset. I.M.W. contributed with model output. All authors discussed the results throughout the study and commented on the manuscript. The authors declare no competing interests.

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