1. Surface Penetrating Radar Simulations for Jupiter’s Icy Moons Thorsten Markus, Laboratory for Hydrospheric Processes NASA/GSFC, Thorsten.Markus@nasa.gov S. Prasad Gogineni, V.C. Ramasami, Univeristy 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). i) Subsurface sounding of solid bodies, to survey ice stratigraphy underlying visible planetologic features and to detect presence and location of regional lakes and lobal oceans ii) Remote magnetospheric sounding, to obtain electron density distributions along the magnetic field line through the spacecraft 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. Possible subsurface structures a) Europa geolocially most active surface mix of rocks and ice ice thickness between 2-30 km (some models 100 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 <3.5ppt, Moore 2000) b) Callisto surface similar to Europa higher percentage of rock ocean possibly deeper than 200 km craters are indicative of lack of subsurface geological processes c) Ganymede rock percentage between Europa and Callisto possible ocean as deep as 800 km 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 Simulations Based on Leuschen et al. (2003) that consists of a) System model: models transmitter and receiver part, incl. generation of waveform b) Propagation model: models propagation c) Geophysical model: models dielectric properties of the media Characteristics: - Frequencies: 1, 2, 5, 10, 20, 50 MHz - Bandwidth: /2 - Pulse: Gaussian 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 Results Reasonble 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 waveform to reduce side lobes and clutter Include surface roughness scenarios and ionospheric effects Typical temperature profiles for cases with and without convection Simulation results for 10 (top) and 20 MHz (bottom). Simulation results for case D using 1, 5, 10, and 20 MHz for convecting (top) and non-convecting (bottom) ice.