Improved Determination of Europa's Long-Wavelength Topography Using Stellar Occultations

Europa Clipper will arrive at Jupiter at the end of this decade and will explore Europa through a series of flybys. One of its many goals is to characterize Europa's topography and global shape using the Europa Imaging System and Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instruments. In addition, Europa Clipper's UV Spectrograph will observe stars pass behind (be occulted by) Europa. The spectrograph has sufficiently precise timing, corresponding to a topographic precision of order meters, that these occultations can also serve as altimetric measurements. Because of gaps in the REASON radar altimeter coverage imposed by the flyby geometries, the addition of similar to 100 occultations results in a substantial improvement in the recovery of Europa's long-wavelength shape. Typically, five extra spherical harmonic degrees of topography can be recovered by combining occultations with radar altimetry.