Investigation of superficial features of the Galilean moons by 3GM experiment aboard ESA JUICE mission

The Geodesy and Geophysics of Jupiter and the Galilean Moons (3GM) experiment aboard the JUpiter ICy moons Explorer (JUICE) will estimate the gravity field of Europa, Callisto (5x5) and Ganymede (40x40). The information about the gravity field can be used to characterize the interior structure of the satellite as well as to identify possible gravity anomalies related to mass concentrations generated by tectonic structures and/or non-homogeneous density distribution within the ice shell. The quadrupole term for Callisto and Ganymede have been set from the Galileo mission; [1,2] for Callisto the higher order terms have been simulated using the Kaula’s rule [3]. With 3GM it will be possible to detect large (thousands of km) surface structures for Callisto, since the data will be acquired only during twelve flybys. While the large amount of data retrieved from the orbital phase will let us to achieve enough detail to potentially identify regional (hundreds of km) structures for Ganymede. Remarkably, the Ganymede’s outer ice shell is characterized by the presence of dark and bright terrains: evidence of older and dirty and younger and clean ice, respectively. We implemented a 3GM simulation to investigate under which conditions (in terms of ice depth and density contrast) it could be possible to detect putative gravity anomalies reflecting the surface distribution of dark and bright terrains. The Ganymede’s gravity field has been generated up to the degree 50, based on the observed distribution of the dark and bright terrains and assuming a density contrast of 50 kg/m3 between the two types of ice and an ice depth of 25 km. With these assumptions, our preliminary results show that 3GM can potentially identify gravity anomalies due to the presence of dark and bright terrains. References: [1] Anderson et al. (2001) - Icarus, 153, 1, 157-161. [2] Anderson et al. (1996) - Nature, 384, 541-543. [3] Bertotti et al. (2003) - Physics of the Solar System, Springer Science+Business-Media.