Study of the ice shells and possible subsurface oceans of the Galilean satellites using laser altimeters on board the Europa and Ganymede orbiters JEO and JGO

Laser altimetry is a powerful tool to map planetary surfaces. In addition to the static topography, timedependent variations such as libration and tidal elevation can be extracted from laser altimeter data in order to investigate the interior structure of the planetary body. The most important objectives of the Europa Jupiter Science Mission (EJSM) proposed in the frame of ESA’s Cosmic Vision Programme are the answer to the question whether the icy Galilean satellites contain subsurface oceans and whether they host habitable worlds. Both the Jupiter Europa Orbiter (JEO) and the Jupiter Ganymede Orbiter (JGO) of EJSM will carry laser altimeters as part of their core scientific payload. In the frame of the BepiColombo Laser Altimeter (BELA) project, we have carried out numerical simulations in order to estimate the uncertainty of the tidal and forced libration amplitudes of Mercury’s surface to be extracted from topography data. These algorithms are now applied to the cases of the JEO and JGO laser altimeters in order to optimize the proposed instrument design for high science return.