1. Sounding the Ganymede’s crust with a GPR V. Ciarletti 1, A. Le Gall 1, M. Biancheri-Astrier 2, J-J. Berthelier 1, S.M. Clifford 3, D. Plettemeier 4, M. Hamelin 1 1 LATMOS, Guyancourt, France 2 IDES, Orsay, France 3 LPI, Houston, TX, USA 4 TUD, Dresden, Germany International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

2. Scientific Objectives Characterize the 3D compositional (ice purity) and physical (porosity, structure) properties of the Ganymede Landing Site down to a depth of ~100m to a few km Identify potential shallow (<1 m depth) and deep (up to ~1+ km) structures Clues to understand the large-scale geologic evolution of the Landing Site Characterize the electromagnetic environment and potential activity of the thin atmosphere (ambient Jovian HF background noise, potential atmospheric discharges ) International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

3. Overview A stationary, impulse, multiband HF GPR operated from the surface designed to conduct geologic investigations of planetary environments in both the near and deep subsurface (~1m – few km) An enhanced version of the low-frequency GPRs developed for The original Mars NetLander (CNES) The original ExoMars mission (mono and bi-static operations) International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

4. The instrument main features Frequency bands 2-4 MHz deep soundings (from 100 m to a few kms with a resolution of ~50m) 3D mapping 3 components of the magnetic field + 2 for the electrical field Retrieval of the direction of arrival of the echoes - 3D mapping of the reflecting structures Modes of operation Active Antenna impedance measurement Passive Detection of weak echoes Deployment on the surface Coherent additions up to 2 28 (in monostatic operation) to improve the SNR International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

5. Mono-static configuration (NetLander) Magnetic sensor Electrical antennas International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

6. Mono & Bi-static configuration (former ExoMars mission) Magnetic sensor Electrical antennas International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

7. Coherent additions efficiency International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

8. Electrical antennas deployed on the surface (transmission and reception) 2 perpendicular dipoles (2 X 35 m long resistively loaded ribbon monopoles) The antennas system Electrical antennas deployment system International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

9. Magnetic antennas (reception) 10 cm long search coil magnetic antenna The antennas system Magnetic sensor International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

10. Demonstration of 3D investigation Mono-Static Investigations of the Subsurface in Antarctic International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

11. Demonstration of 3D investigation Mono-Static Investigations of the Subsurface in Antarctic Topography reconstruction International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

12. Application to Ganymede International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments” In active mode: Assessing the stratigraphy of a grooved terrain, a crater or a putative cryo-volcanic features on Ganymede will significantly help to determine and describe the geological processes that have shaped the moon’s surface and bring new constraints on its age.

13. Application to Ganymede International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments” In active mode: could contribute greatly to the understanding of the relationship between this subsurface ocean and the surface by revealing compositional boundaries between different ice sheets.

14. Application to Ganymede International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments” In the antenna impedance measurement mode: will help to characterize Ganymede’s crust composition and in particular the proportion of non-ice components in the near surface. εr=3σ=10 -5 S/m Simulation ε r ~3 σ~10 -5 S/m Measurement Simulation Electrical HF antenna impedance measurement

15. Application to Ganymede International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments” Passive mode: will monitor Jupiter radiation and its variations with time. Better to operate on the anti-Jupiter side of Ganymede!

16. Summary The data acquired by such low-frequency GPR will provide local information about the geology of the Landing site: at a scale (~100 m – a few kms) and resolution (~10 – 100 m) including its composition, stratigraphy and structure. International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

17. Back up slides

18. Mono-Static HF measurements Passive measurements Impedance measurements Magnetic sensor Electrical antenna Bi-Static HF measurements Mono & Bi-static configuration (former ExoMars mission) International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”

19. Demonstration of 3D investigation Bi-Static Investigations of the Subsurface 1st interface 2nd interface 3rd interface Tx In profile: International Colloquium and Workshop “Ganymede Lander: scientific goals and experiments”