Plasma measurements at and on Ganymede

Plasma measurements at and on Ganymede

O. Vaisberg, D. Moiseenko, G. Koynash, A. Shestakov, and R. ZhuravlevSPACE RESEARCH INSTITUTE, RUSSIAN ACADEMY OF SCIENCES, RUSSIA

A.J. Coates, G.H. Jones, C.S. Arridge, D.O. KatariaMULLARD SPACE SCIENCE LABORATORY, UNIVERSITY COLLEGE LONDON, UK

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

MotivationGanymede 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"

JOVIAN AURORA AND FOOTPRINTS OF SATELLITES

FOOTPRINT OF GANYMEDE

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

Auroral footprint of Ganymede is produced by electric currents generated by motion of the satellite relative Jovian magnetic field. This current flows along Jupiter's magnetic field lines and exites the glow of the upper atmosphere. This ultraviolet image of Jupiter was taken with the Hubble Space Telescope Imaging Spectrograph (STIS) on November 26, 1998.

Facts about GanymedeTenuous oxygen atmosphere of 1.2 × 108–7 × 108 cm−3 and hydrogen atoms of ~ 1.5 × 104 cm−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"

Magnetospheric plasma near Ganymede

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

Measurements requirementsMagnetosphere of Ganymede

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

Combination of internal and induced magnetic fields -> open magnetosphere

Scientific goals of experimentGanymede’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 GanymedeIon composition of plasma and accelerated particles Ganymede’s role in magnetospheric plasma population Magnetospheric plasma dynamicsElectromagnetic interaction with Jupiter

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

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"

Prototype: energy-mass analyzer RIP-803 on Prognoz-2

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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"

Structure and simulation results1

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Structure of the instrument:

1 – angular scanner,2 – electrostatic analyzer,3 – drift tube,4 – magnet,5 – focusing electrode,6 – MCP detector

Simulation results for solar wind ions Fe+7- Fe+12 and O+5 and O+6 with E/Q = 1 keV (1…20 keV/Q capability)

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

Characteristics of prototype under development

Energy range, keV/Q 1…20Mass range, M/Q 2…9Mass resolution, M/Δm 10-40 for E/Q = 1 keVFull angle of view 300х300 for E/Q = 1 keVAngular resolution ~20

Analyzer dimensions, mm 230х170х120Estimated mass, kg 3.5

International Colloquium and Workshop "Ganymede Lander: scientific goals and experiments"

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"