The magnetic world of Ganymede: an assessment of cross-magnetopause energy transport and its effects on the only known moon magnetosphere
File(s)
Author(s)
Kaweeyanun, Nawapat
Type
Thesis
Abstract
Ganymede – Jupiter’s largest moon – generates a permanent magnetic field due to its Earth-like molten iron core. The internal magnetism affords Ganymede its own magnetosphere that is encased by Jupiter’s field-carrying plasma sheet at all times. However, this unique magnetic domain remains poorly understood due to insufficient observational data. This thesis provides fundamental assessments on aspects of Ganymede’s magnetosphere through analytical modelling, and offers baseline predictions for future observations of the moon.
The first work chapter considers the upstream magnetopause, where magnetic reconnection is expected to drive Dungey-like plasma convection in Ganymede’s magnetosphere. I evaluate magnetic reconnection onset to be favourable across the entire boundary, with average rates exhibiting Jovian half-synodic variation consistent with governance by Jupiter’s rotation. The second work chapter then determines that magnetopause reconnection is significantly localised as flux-transfer events, and sufficiently rapid that Ganymede’s magnetotail must also contain rapid reconnection site(s) to maintain a stable magnetosphere.
The third work chapter returns to the magnetopause and assesses Ganymede’s Kelvin-Helmholtz (K-H) instability growth. Linear K-H waves are expected to form along magnetopause flanks, with notable inter-flank asymmetry due to finite Larmor radius effects. However, nonlinear K-H vortex growth should be suppressed by concurring reconnection events, limiting the instability’s role in Ganymedean plasma convection. Finally, the fourth work chapter estimates the magnetopause’s Chapman-Ferraro (C-F) magnetic field, which varies at Jovian half-synodic period corresponding with near-boundary conditions. The C-F signal is shown to induce a secondary magnetic response from Ganymede’s subsurface ocean of magnitude ~1-10 nT, which is resolvable by modern magnetometers and establishes the magnetopause as a potential probe for ocean study via magnetic induction.
The thesis concludes with introduction of the upcoming JUpiter ICy moon Explorer mission, which will not only verify predictions from the work chapters, but also exponentially advance our understanding of Ganymede as a whole.
The first work chapter considers the upstream magnetopause, where magnetic reconnection is expected to drive Dungey-like plasma convection in Ganymede’s magnetosphere. I evaluate magnetic reconnection onset to be favourable across the entire boundary, with average rates exhibiting Jovian half-synodic variation consistent with governance by Jupiter’s rotation. The second work chapter then determines that magnetopause reconnection is significantly localised as flux-transfer events, and sufficiently rapid that Ganymede’s magnetotail must also contain rapid reconnection site(s) to maintain a stable magnetosphere.
The third work chapter returns to the magnetopause and assesses Ganymede’s Kelvin-Helmholtz (K-H) instability growth. Linear K-H waves are expected to form along magnetopause flanks, with notable inter-flank asymmetry due to finite Larmor radius effects. However, nonlinear K-H vortex growth should be suppressed by concurring reconnection events, limiting the instability’s role in Ganymedean plasma convection. Finally, the fourth work chapter estimates the magnetopause’s Chapman-Ferraro (C-F) magnetic field, which varies at Jovian half-synodic period corresponding with near-boundary conditions. The C-F signal is shown to induce a secondary magnetic response from Ganymede’s subsurface ocean of magnitude ~1-10 nT, which is resolvable by modern magnetometers and establishes the magnetopause as a potential probe for ocean study via magnetic induction.
The thesis concludes with introduction of the upcoming JUpiter ICy moon Explorer mission, which will not only verify predictions from the work chapters, but also exponentially advance our understanding of Ganymede as a whole.
Version
Open Access
Date Issued
2022-05
Date Awarded
2022-09
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Masters, Adam
Sponsor
Royal Society (Great Britain)
Grant Number
RGF\EA\180226
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)