A study on Ganymedeʹs surface topography: Perspectives for radar sounding

Radar sounding of Jovian icy satellites has great potential to address specific science questions such as the presence of subsurface liquid water. Radargrams acquired over Mars polar caps allow observing clear echoes up to kilometers depth. However, Jovian icy satellites display dramatically different surface topographies. In order to assess possible issues arising from such surface topographies on radar sounding, we performed a study on different DEMs (Digital Elevation Models) obtained on Ganymede. Topographic data are derived using stereo and photoclinometric analysis of Galileo and Voyager images at resolutions of 16–629 m. Main results are presented in this paper. Overall we found that Ganymedeʹs surface is quite rough, with mean slopes at 630 m scale varying from 3.5° to 8°, smoothest terrains being found within sulcii. This will be a major challenge for the design of radar sounders and parameters should be chosen accordingly in order to correctly sound this planetary body. Previous studies have shown similar concern for Europa.