Plasma measurements at and on Ganymede

1. Plasma measurements at and on Ganymede • O. Vaisberg, D. Moiseenko, G. Koynash, A. Shestakov, and R. Zhuravlev • Space Research Institute, Russian Academy of Sciences, Russia • A.J. Coates, G.H. Jones, C.S. Arridge, D.O. Kataria • Mullard Space Science Laboratory, University College London, UK International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

2. Motivation Ganymede is composed of rock and ice. It has intrinsic magnetic field, that makes it an exciting object for investigation. Its plasma composition is c consists of Jupiter magnetospheric particles and ions originated from the surface of Ganymede. Interaction of Ganymede’s and Jovian magnetospheres leads to acceleration of ions and complicated transport. Analysis of ion flux, composition and velocity distribution provides important tool for Ganymede’s soil composition and characteristics, not only on local scale but also on planetary scale, due to transport within Ganymede’s environment. International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

3. JOVIAN AURORA AND FOOTPRINTS OF SATELLITES Footprint of Ganymede Auroralfootprint ofGanymedeisproducedbyelectriccurrentsgeneratedbymotion of thesatellite relative Jovian magnetic field. This current flowsalongJupiter'smagneticfield lines and exites the glow oftheupperatmosphere. ThisultravioletimageofJupiterwastakenwiththeHubbleSpaceTelescopeImagingSpectrograph (STIS) onNovember 26, 1998. International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

4. Facts about Ganymede Tenuous oxygen atmosphere of 1.2 × 108–7 × 108 cm−3and hydrogen atoms of ~ 1.5 × 104cm−3 Intrinsic magnetic moment is about 1.3 × 1013 T·m3 directed against the Jovian magnetic moment. 720 nT at equator (Jovian magnetic field 120 nT). Moves relative to Jovian magnetic field with subsonic velocity. Its magnetosphere has diameter is 4–5 RG (RG = 2,631.2 km) Ganymede has airglow near ± 50° latitude, which is exactly the boundary between the open and closed field lines of the Ganymedian magnetosphere Relative motion induces magnetic field that suggests highly conducting ocean. Energetic electrons and ions (tens and hundreds of kiloelectronvolts) hit Ganymede’s surface that leads to sputtering International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

5. Magnetospheric plasma near Ganymede International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

6. Measurements requirements Magnetosphere of Ganymede Combination of internal and induced magnetic fields -> open magnetosphere International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

7. Scientific goals of experiment Ganymede’s surface and atmosphere Atmospheric/ion composition and its losses to the magnetosphere Fluxes of accelerated ions and electrons near Ganymede and/or at its surface. Surface sputtering and implantation of energetic ions Mapping of surface composition Jovian magnetosphere and its interaction with Ganymede Ion composition of plasma and accelerated particles Ganymede’s role in magnetospheric plasma population Magnetospheric plasma dynamics Electromagnetic interaction with Jupiter International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

8. Proposed ion spectrometer Measurements of flux and velocity distribution of suprathermal and energetic ions, and mass/charge ion composition for investigation: - influence on Ganymede’s surface - surface composition - Ganymede’s atmospheric losses - composition of Ganymede and its atmosphere - Jovian magnetospheric plasma dynamics and the role of Ganymede in Jovian magnetosphere International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

9. Prototype:energy-mass analyzer RIP-803 on Prognoz-2 3 1 2 4 8 9 5 7 6 1 – collimator, 2 – electrostatic analyzer, 3 – light trap,4 – diaphragm, 5 – wedge magnet, 6 – drift tube,7 – grids, 8 – secondary electron multiplier (SEM),9 – DC amplifier,10 – pulse counter Velocity distributions of proton- and α-s measurements in May 1972. International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

10. Structure and simulation results 1 Structure of the instrument: 1 – angular scanner, 2 – electrostatic analyzer, 3 – drift tube, 4 – magnet, 5 – focusing electrode, 6 – MCP detector 2 3 4 Simulation results for solar wind ions Fe+7- Fe+12and O+5 and O+6 with E/Q = 1 keV (1…20 keV/Q capability) 5 6 International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

11. Characteristics of prototype under development International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

12. Conclusion • Measurements of ions, electrons and secondary neutral particles provide important tools for investigation of Ganymede’s surface characteristics and composition • Ion spectrometer under development can be considered as candidate for plasma suite developed by MSSL and IKI for exploration of planetary surfaces and planetary magnetospheres International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"