Ionosphere of Ganymede: Galileo observations versus test particle simulation
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Published version
Author(s)
Type
Journal Article
Abstract
In this paper, we model the plasma environment of Ganymede by means of a collisionless test particle simulation. By coupling
the outputs from a Direct Simulation Monte Carlo (DSMC) simulation of Ganymede’s exosphere (i.e. number density profiles of
neutral species such as H, H2, O, HO, H2O, O2 for which we provide parametrization) with those of a MagnetoHydroDynamic
simulation of the interaction between Ganymede and the Jovian plasma (i.e. electric and magnetic fields), we perform a
comparison between simulated ion plasma densities and ion energy spectra with those observed in situ during six close flybys of
Ganymede by the Galileo spacecraft. We find that not only our test particle simulation sometimes can well reproduce the in situ
ion number density measurement, but also the dominant ion species during these flybys are H+
2 , O+
2 , and occasionally H2O+.
Although the observed ion energy spectra cannot be reproduced exactly, the simulated ion energy spectra exhibit similar trends
to those observed near the closest approach and near the magnetopause crossings but at lower energies. We show that the neutral
exosphere plays an important role in supplying plasma to Ganymede’s magnetized environment and that additional mechanisms
may be at play to energize/accelerate newborn ions from the neutral exosphere.
the outputs from a Direct Simulation Monte Carlo (DSMC) simulation of Ganymede’s exosphere (i.e. number density profiles of
neutral species such as H, H2, O, HO, H2O, O2 for which we provide parametrization) with those of a MagnetoHydroDynamic
simulation of the interaction between Ganymede and the Jovian plasma (i.e. electric and magnetic fields), we perform a
comparison between simulated ion plasma densities and ion energy spectra with those observed in situ during six close flybys of
Ganymede by the Galileo spacecraft. We find that not only our test particle simulation sometimes can well reproduce the in situ
ion number density measurement, but also the dominant ion species during these flybys are H+
2 , O+
2 , and occasionally H2O+.
Although the observed ion energy spectra cannot be reproduced exactly, the simulated ion energy spectra exhibit similar trends
to those observed near the closest approach and near the magnetopause crossings but at lower energies. We show that the neutral
exosphere plays an important role in supplying plasma to Ganymede’s magnetized environment and that additional mechanisms
may be at play to energize/accelerate newborn ions from the neutral exosphere.
Date Issued
2025-04-01
Date Acceptance
2025-02-17
Citation
Monthly Notices of the Royal Astronomical Society, 2025, 538 (4), pp.2483-2507
ISSN
0035-8711
Publisher
Oxford University Press
Start Page
2483
End Page
2507
Journal / Book Title
Monthly Notices of the Royal Astronomical Society
Volume
538
Issue
4
Copyright Statement
© 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
10.1093/mnras/staf313
Subjects
MHD -plasmas -methods
numerical -planets and satellites
atmospheres -planets and satellites
individual
Ganymede
Publication Status
Published
Date Publish Online
2025-02-25