Surface Penetrating Radar Simulations for Europa

1
Surface Penetrating Radar Simulations for
Europa Thorsten Markus, Laboratory for
Hydrospheric Processes NASA/GSFC,
Thorsten.Markus_at_nasa.gov S. Prasad Gogineni, V.C.
Ramasami, University of Kansas, Lawrence, KS J.
Green, S.F. Fung,, J.F. Cooper, W.W.L. Taylor,
Space Science Data Operations Office,
NASA/GSFC B.W. Reinisch, P. Song, University of
Mass., Lowell, MA R.F. Benson, Laboratory f.
Extraterrestrial Physics, NASA/GSFC D. Gallagher,
NASA/MSFC
Introduction As part of the planned Jupiter Icy
Moons Orbiter (JIMO) mission as proposal has been
submitted for the development of a radio sounder
that operates at the frequency range from 1 kHz
to 50MHz. With this instrument five fundamental
scientific measurements can be made (Figure 1).

• Possible subsurface structures
• geolocially active
• surface mix of rocks and ice
• ice thickness between 2-30 km
• Convective or non-convective ice layer
• (if convective maximum thickness 20 km Moore,
  2000)
• does ice contain salt?
• dome-shaped features are a result of diapirism
  (Nimmo and Manga, 2003)
• ocean most likely salty (although expexted to be
  small lt3.5ppt, Moore 2000)
• Radar considerations
• - Direct detection of ocean only possible for
  Europa
• - Radar signatures, though, can yield information
  about subsurface
• structures that may again reveal indirect
  indications of the presence of
• an ocean
• Simulation

Some Europa scenarios A -thin frost layer
- 2.1 km of ice with 5 rocks - 4.9 km of
saline ice (convecting or non-convecting) -
bedrock underneath B - thin frost layer -
2.1 km ice with 5 rocks - 4.9 km of saline
ice (convecting or non-convecting) - ocean
underneath C - thin frost layer - 2.1 km
ice with 5 rocks - 4.9 km of pure ice
(convecting or non-convecting) - ocean
underneath D - thin frost layer - 2.1 km
ice with 5 rocks - 4.9 km of pure ice
(convecting or non-convecting) - bedrock
underneath
Simulation results for 10 (top) and 20 MHz
(bottom).
i) Subsurface sounding of solid bodies, to survey
ice stratigraphy underlying visible surface
features and to detect presence and location of
regional lakes and global oceans. ii) Remote
magnetospheric sounding, to obtain electron
density distributions along the magnetic field
line through the spacecraft, and length of local
field lines connecting to moon
ionospheres. iii) Remote sounding of moon
ionospheres, to measure altitude profiles of
electron density below the spacecraft at points
along its orbit. iv) Local sounding, to
determine the magnetic field strength and the
electron density at the spacecraft. v) Passive
electric field observations, to measure natural
electromagnetic and electrostatic emissions.
Typical temperature profiles for cases with and
without convection. With convection, the sea ice
layer is essentially isothermal and a
strong temperature gradient exist in the upper
layer. Without convection there is a more gradual
temperature gradient.

• Results
• Reasonable return signals
• Distinct differences between ocean and bedrock
  in the simulations
• Differences between convecting and
  non-convecting ice
• (loss is greater for convecting ice)
• Issues
• Determine dielectric properties that are valid
  for conditions at these moons
• a) to develop more accurate model
• b) to accurately adjust velocity of light
  depending on media
• (calculation of depth from time signal)
• Analyze different waveforms to reduce side lobes
  and clutter
• Include different surface roughness scenarios
  and ionospheric effects

Summary of applications
Simulation results for case D using 1, 5, 10, and
20 MHz for convecting (top) and non-convecting
(bottom) ice.