Analysis of Ganymede rotational state using JANUS telescope

Ganymede as well as Europa and Callisto are thought to present a complex internal structure comprising a sub-surface ocean. The thickness of its ice shell, the presence and depth of the liquid layer as well as the details about the interior structure have not been well constrained. Direct measurement of librational motion of Ganymede will be a useful tool for detecting an ocean and characterizing the interior parameters of this moon. JUICE high-resolution camera images will be used to track landmarks on the surface of this body and measure their longitudinal shift. Goal of this work is to define an error budget for such kind of measurements, investigate to which extent the libration can be detected and define both the algorithms and the observational strategies that could be used for this analysis.