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TITLE
CERTIFICATE
DECLARATION
DEDICATION
ACKNOWLEDGEMENT
CONTENTS
PREFACE
Publications
Conference Presentations
1. INTRODUCTION
1.1. About Io
Table 1.1. Physical characteristics of Io
Fig.1.1. Close-up color view (false color composite) of Io takerl by Galileo SSI. The yellow, brown and red patches represent different sulfur -based minerals. Bright patches are sulfur dioxide rich regions.
1.1.1. Geophysics of Io
Fig.1.2. A currently suggested schematic of the interior structure of lo.
Fig.1.3 (a) The gravity of Jupiter and large moon Ganymede
Fig.1.4. The Galileo SSI image of eruption plume over Pillan Patera
Fig.1.5. The close up view of Ra Patera, a large shield volcano, taken by Voyager spacecraft, shows colourful flows up to about 300 km long emanating from the dark central volcanic vent
Fig.1.6. Galileo SSI image of Io in eclipse (PIC No. C910026) The bright spots in this image indicate the locations of volcanic vents on Io, which are spewing hot lava.
1.1.2. Atmosphere of Io
1.2. Io-Torus-Jovian Magnetosphere Interaction
Fig. 1.7. A schematic of the Jupiter-10- torus system.
1.3. Electron Degradation Techniques
1.4. About the Thesis
2. ELECTRON IMPACT CROSS SECTIONS
2.1. Introduction
2.2. Cross Sections for Electron Impact on SO2
2.2.1. Total
2.2.2. Elastic
2.2.2.1. Differential Elastic
Fig.2.1. The electron impact cross sections of SO, for all inelastic and elasticprocesses.
Table 2.1. Cross Sections of Various Processes of Electron Impact of SO2
2.2.2.2. Total Elastic
Fig.2.2 (a) Differential elastic cross sections of SO2 as a function of scattering angle at energies 1, 2, 3.4, 5, 10, and 12eV.
Fig.2.2 (b) Same as (a) for energies 15, 20, 30, 50, 100, and 200 eV
2.2.3. Dissociative Electron Attachment
Table 2.2. Parameters for elecron Attachment Processes for SO2
2.2.4. Ionization
Fig.2.3. Electron attachment cross sections. Symbols represent the measured values
Table 2.3. Parameters for Ionization Processes for SO2
Fig.2.4. Ionization cross sections. Symbols represent the measured values
2.2.5. Excitation
2.2.6. Middle Ultraviolet Emissions
Fig.2.5. Cross sections for the various excited bands.
2.2.7. EUV and FUV Emissions
Fig.2.6. The Cross sections for The MUVl and MUV2 events.
Table 2.5. Parameters for EUV and FW Emission Lies for SO2
2.2.8. Vibrational Excitation
Fig.2.7. Cross sections for the various emission lines.
2.3. Cross Sections for Electron Impact on Atomic Oxygen
2.3.1. Total
2.3.2. Elastic
Fig.2.8. The electron impact cross sections of O for all inelastic and elastic processes.
Table 2.6. Cross Sections of Vanous Processes of Electron Impact on O
2.3.3. Ionization
2.3.4. Excitation and Emission
2.3.4.1. 1356 A emission
2.3.4.2. 1304 A emission
Fig.2.9. The electron impact cross sections of O producing OI (1304 A), OI (1356 A) OI (6300 A), OI (5577 A) emission lines.
2.3.4.3. Excitation to D and S states
2.4. Summary
3. MODEL FOR ELECTRON DEGRADATION IN SO2 GAS
3.1. Introduction
3.2. Monte Carlo Model
Fig.3.1. The flow diagram of successive procedures followed in the Monte Carlo simulation,
3.3. Yield Spectra
Fig. 3.2. The analytical yield spectra (solid lines) and the numerical yield spectra
3.4. Mean Energy per Ion Pair
3.5. Production of Secondary Electrons
Fig.3.3. The mean energy per ion pair for the ions SO2, SO, S, O, 0 and theneutral SO2 gas (marked as total)
Fig.3.4. The energy distribution of secondary electrons at four incident energies (h)
3.6. Efficiency
Fig.3.5. Efficiencies of various ionization events.
Fig.3.6. Efficiencies of various bands excitations.
Fig.3.7. Efficiencies of neutral atomic oxygen line emissions. The wavelength given in parentheses are in A.
Fig.3.8. Efficiencies of neutral atomic oxygen and sulfur line emissions. The wavelengths given in parentheses are in A.
Fig.3.9. Efficiencies of singly ionized oxygen emissions. The wavelengths given in parentheses are in A.
Fig.3.10. Efficiencies of singly ionized sulfur emissions. The wavelengths given in parentheses are in A.
Fig. 3.11. Efficiencies of electron attachment processes.
Fig.3.12. Efficiencies of various loss channels grouped into important processes
3.7. Inclusion of Dissociation Process in the Model
3.7.1. Dissociation Cross Sections
Fig.3.13. Dissociation cross sections estimated using the dissociation to excitation cross section (DECS) ratios of O2, (line with solid circles), N2 (line with crosses), and H2O (line with open diamonds)
3.7.2. Effects of Including Dissociation Process
Fig.3.14. Efficiency of the dissociation process calculated using all the three estimated cross sections.
Fig.3.15. Efficiencies of various important loss channels after including dissociation as a separate process.
3.8. Summary
4. PHOTOIONIZATION OF IOS ATMOSPHERE
4.1. Introduction
4.2. Cross Sections
4.2.1. Photo absorption Cross Section
4.2.2. Photo ionization Cross Section
Fig.4.1 Photoabsorption cross sections of SO2 reported by Wu and Judge (1981), Hamdy ct al. (1991)Cooper (1991) and Holland (1995)
Fig.4.2 The photoabsorption (ABS) and photoionization cross sections of SO2 forming SO2+, SO+, S+, O2+ and O+ ions.
Table 4.1. Photoabsorption and Photoionization cross sections of SO2 averaged at 37 wavelengths
4.3. Solar Flux
4.4. Photo ionization Rates
Table 4.2. Solar Flux Averaged at 37 Wavelength Intervals
Table 4.3. Photodissociative Ionization Rates for SO2 at 1 AU in s-1
4.5. Ion production Rates in Ios atmosphere
4.5.1. Photodissociative Ionization of SO2
4.5.2. Direct Photo ionization of SO,0, S, and O2
Fig.4.3. The production rates of SO2+ ion. Solid line represents the production rate due to photoionization of SO2
Fig.4.4. The production rates of SO+ ion.
Fig.4.5. The production rates of O+ ion.
Fig.4.6. The production rates of S+ ion.
Fig 4.7. The production rates of O2+ ion.
4.5.3. Photoelectron Impact Dissociative Ionization of SO2
Fig.4.8. The photoelectron energy spectrum on Io at three altitudes.
4.5.4. Discussion
4.6. Conclusions
5. PHOTOELECTRON EXCITATION OF IOS ATMOSPHERE
5.1. Introduction
5.2. Model Atmospheres
Fig.5.1 (a) Neutral SO2 and O densities in the atmosphere of Io from Kumar (1982) .
Fig.5.1 (b) Neutral SO2 and O densities in the atmosphere of Io from Summers Strobel (1996) .
5.3. Photoelectron Flux
Fig.5.1 (c) Neutral SO2 and O densities in the atmosphere of Io from Wong and Johnson (1996) .
5.4. Observed UV Emissions on Io
Fig.5.2. Photoelectron flux calculated using Monte Carlo (solid lines) and Analytical Yield Spectra (dotted lines) models at 3 altitudes in the Ios atmosphere.
5.5. Calculated UV Emissions and Discussion
Fig.5.3. Volume Emission Rate profiles of OI (1304 A) produced by e-SO2 (dashed line) and e-O (solid line) collisions using the model atmosphere of Wong and Johnson (1996)
Fig.5.4. Same as Figure 5.3 for the model atmosphere of Summers and Strobel (1996)
Fig.5.5. Same as Figure 5.3 for the model atmosphere of Kumar (1982)
Table 5.1. Calculated Column and Observed Intensities on Io in Rayleigh
Fig.5.6. Volume emission rate profile of OI (1304 A) produced via e-SO2 collision, assuming all the photoelectrons are of 100 eV, using the model atmosphere of Wong and Johnson (1996)
Fig.5.7. Neutral densities of SO2 and O in the Ios atmosphere generated in the present study.
Fig.5.8. Volume Emission Rate profiles of OI (1304 A) produced by e-O collision using the model atmosphere presented in Figure 5.7 for solar minimum and solar maximum conditions.
Table 5.2. Calculated Column and Averaged intensities of Emissions on Io in Rayleigh
5.6. Conclusions
Fig.5.9. Same as that of Figure 5.8 assuming all photoelectrons are of 100 eV.
6. EXCITATION OF IOS ATMOSPHERE BY FIELD ALIGNED ELECTRONS
6.1. Introduction
Fig.6.1. Galileo Energetic Particle detector (EPD) observed magnetically field aligned electron flux during closest approach of Io on 7, December 1995 at 1745: 46 UT.
Fig.6.2. Galileo Plasma Science (PLS) instrument observed magnetically field aligned electron flux during closest approach of Io on 7, December 1995 at 1746: 43 UT.
6.2. Model Calculation
Fig. 6.3. Electron impact cross section of Na producing 5890+5896 A emission.
6.3. Excitation of Ios Atmosphere: Results
6.3.1. Monoenergetic Electrons
Fig.6.4. Number density of Na in the 10s atmosphere taken from Summers andStrobel (1996)
Fig.6.5. Volume emission rate profiles of OI (1304 A)
Fig.6.6. Same as Figure 6.5 for model atmosphere of Summers and Strobe1 (1996)
Table 6.1. Columi Production Rates in cm-2 S-1 for Monoenergetic Unit Electron Flux
6.3.2. Galileo EPD-Observed Electron Flux
Fig.6.7. Volume emission rate profiles of OI (1304 A) and OI (1356 A)
Fig.6.8. Volume emission rate profiles of violet band, OI (6300 A), OI (5577 A), and Na (5890 A), lines obtained using the electron flux observed by EPD for the model atmosphere of Wong and Johnson (1996)
Fig.6.9. Volume emission rate profiles of IOI (1304 A) and OI (1356 A)
Fig.6.10. Volume emission rate profiles of violet band, OI (6300 A), OI (5577 A), and Na (5890 A) lines
Table 6.2. Model Calculated and HST-Observed Disk-Averaged Intensities of FUV Emissions on IO
Table 6.3. Model C: alculated and Galileo SSI-Observed Disk-Averaged Intensities of Visible Emissions on Io
6.3.3. Galileo PLS-Observed Electron Flux
Fig.6.11. Volume emission rate profiles of OI (1304 A) and OI (1356 A)
Fig.6.12. Volume emission rate profiles of violet band, OI (6300 A), OI (5577 A), and Na (5890 A),
Fig.6.13. Volume emission rate profiles of OI (1304 A) and OI (1356 A)
Fig.6.14. Volume emission rate profiles of violet band
6.4. Discussion
Fig.6.15. Volume excitation rate of the metastable atomic oxygen [O (1D) ] and the volume emissron rate profiles of OI (6300 A),
Fig.6.16. Volume excitation rate of the metastable atomic oxygen [O (1D) ] and the volume emission rate profiles of OI (6300 A)
6.5. Correlation between Emissions of Io and Jupiter
6.6. Conclusion
REFERENCES