Investigation of the Magnetosphere of Ganymede with Galileo's Energetic Particle Detector

Ph.D. dissertation by Shawn M. Stone, University of Kansas, 1999.

Copyright 1999 by Shawn M. Stone.  Used with permission.

Abstract

This work evaluates the magnetic field models that represent the magnetosphere of Ganymede using absorption signatures observed by the Energetic Particle Detector (EPD) during the G2 and G7 encounters. The first model, presented by Kivelson et al. [1996] and hereafter denoted as model M1, is derived from the residual G1 encounter magnetic field data after the KK96 background field [Khurana, 1997] is extracted. The result is a simple dipole with surface strength 750 nT at the equator, with the magnetic moment tilted by 10° towards 200° east longitude. The second model, denoted as model M2, is derived in this dissertation from the G2 magnetic field data (the closest flyby) with a background field obtained from a statistical average of the field outside the magnetopause boundary removed. The residual is fit to an internal multipole model for Ganymede to order n=2 (quadrapole), and a magnetopause/tail configuration according to Choe and Beard [1973, 1974] to order n=2.

The evaluation of these models is done by the time reversed following of charged particles from the EPD detector through the configuration of these two models. Particles that intersect the surface of Ganymede are removed from the distribution of particles. In this manner a simulated rate profile can be generated and compared to the actual one measured by the EPD. Not only will this serve to test the validity of the two magnetic field models, but also the effects of mechanisms such as corotational and parallel electric field, and pitch angle scattering effects on the absorption signatures to infer their presence and extent. We will show that model M1 is adequate during the closest approach phase of the G2 encounter, but has trouble in the inbound phase and outbound phase. At G7, model M1 does not recover the absorption features consistently. Model M2 does a better job throughout both the G2 and G7 encounters, recovering the presence and depth of most of the features without the addition of any other mechanisms. This will be shown to be due to the overestimation of the Ganymede magnetic field surface strength of model M1. The presence of the magnetopause and tail fields relaxes the requirement that the internal field model fit the data. It will also be shown that the presence of scattering is indeed necessary to recover the shape of the loss cone and bounce shadow features during the closest approach and outbound phase of the G2 encounter and for the entire G7 encounter. The presence of corotational and parallel electric fields within the magnetosphere of Ganymede will be ruled out.

• Dedication and Acknowledgments
• Chapter 1 Introduction
• Chapter 2 Single Particle Theory
• Chapter 3 Instrument Characteristics and Coordinate Systems
• Chapter 4 Magnetic Field Models
• Chapter 5 The Simulation: Time Reversed Particle Following
• Chapter 6 Time Reversed Particle Results:  G2 Encounter
• Chapter 7 Corotational & Parallel Electric Fields:  G2 Encounter
• Chapter 8 Discussion and Conclusions
• References
• Appendix A The SPICE Kernel System
• Appendix B G7 Results
• Appendix C Additional G2 Results
• Appendix D (C Code, Fortran, Mathematica)

→ Detailed Outline (subsections, figures, tables; not part of original dissertation)
→ List of Tables (not part of original dissertation)
→ List of Figures (not part of original dissertation):
          • Figures Part 1, Chapters 1-5
          • Figures Part 2, Chapter 6
          • Figures Part 3, Chapters 7-8
          • Figures Part 4, Appendix B
          • Appendix C, over 100 additional G2 figures, captioned only by group

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