Investigating the interior of Ganymede, Callisto and Europa with JUICE

On 14 April 2023, the JUpiter ICy moons Explorer (JUICE) of ESA was launched from Europe's Spaceport in French Guiana. It will arrive at Jupiter and its moons in July 2031. Here we describe how JUICE will investigate the interior of the three icy Galilean moons, Ganymede, Callisto and Europa. Best insights into their interior, such as from an induced magnetic field, tides, rotation variations, and radar reflections, will be obtained during close flybys of the moons with altitudes of about 1000 km or less and during the Ganymede orbital phase at an average altitude of about 500 km and less. The 9-month long orbital phase around Ganymede, the first of its kind around another moon than our moon, will allow an unprecedented and detailed insight into the moon’s interior, from the central regions where a magnetic field is generated to the internal ocean and outer ice shell. Multiple flybys of Callisto will constrain the density structure, clarify the differences in evolution compared to Ganymede and will provide key constraints on the origin and early evolution of the Jupiter system. JUICE will visit Europa only during two close flybys and will perform geophysical investigations on selected areas, complementary to those performed by Europa Clipper.We emphasize the synergistic aspects of the different geophysical investigations, showing how different instruments will work together to probe the hydrosphere, internal differentiation, dynamics, and evolution of these icy moons. In situ measurements and remote sensing observations will support the geophysical instruments to achieve these goals by providing complementary information about tectonics, potential plumes, surface composition, and exchange processes between ocean, ice and surface. Additional insight into the dissipative processes in the Jupiter system will be provided by accurate tracking of the JUICE spacecraft.