Particle-in-cell simulations of the Cassini spacecraft’s interaction with Saturn’s ionosphere during the Grand Finale
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Author(s)
Zhang, Z
Desai, R
Miyake, Y
Usui, H
Shebanits, O
Type
Journal Article
Abstract
A surprising and unexpected phenomenon observed during Cassini’s Grand Finale was the spacecraft charging to positive potentials in Saturn’s ionosphere. Here, the ionospheric plasma was depleted of free electrons with negatively charged ions and dust accumulating up to over 95 per cent of the negative charge density. To further understand the spacecraft–plasma interaction, we perform a three-dimensional Particle-In-Cell study of a model Cassini spacecraft immersed in plasma representative of Saturn’s ionosphere. The simulations reveal complex interaction features such as electron wings and a highly structured wake containing spacecraft-scale vortices. The results show how a large negative ion concentration combined with a large negative to positive ion mass ratio is able to drive the spacecraft to the observed positive potentials. Despite the high electron depletions, the electron properties are found as a significant controlling factor for the spacecraft potential together with the magnetic field orientation which induces a potential gradient directed across Cassini’s asymmetric body. This study reveals the global spacecraft interaction experienced by Cassini during the Grand Finale and how this is influenced by the unexpected negative ion and dust populations.
Date Issued
2021-06-01
Date Acceptance
2021-03-08
ISSN
0035-8711
Publisher
Royal Astronomical Society
Start Page
964
End Page
973
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
504
Issue
1
Copyright Statement
©The Author(s) 2021.Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the CreativeCommons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium,provided the original work is properly cited.
Sponsor
Natural Environment Research Council (NERC)
Grant Number
NE/P017347/1
Subjects
physics.space-ph
physics.space-ph
astro-ph.EP
astro-ph.IM
physics.plasm-ph
Astronomy & Astrophysics
0201 Astronomical and Space Sciences
Publication Status
Published
Date Publish Online
2021-03-13