Science Opportunities with a Double-Langmuir Probe Experiment for the Jupiter Icy Moons Orbiter

The three icy Galilean moons of Jupiter, Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. All three moons have thin atmospheres of mostly molecular oxygen probably arising from magnetospheric ion bombardement sputtering of their water-ice surfaces. The atmospheres and their ionized ionospheric components interact strongly with the co-rotating magnetosphere of Jupiter. The residence times for their atmospheres are of the order of a few days at most. The estimated peak electron densities varies between 1,000-10,000 cm(-3) near their surfaces, and the ionosphere of Callisto seems highly variable in time. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. The surface-interactions with the space environment determine the atmospheric and ionospheric properties (e.g., density, composition, and temperature), which offer an opportunity to investigate the weathering properties of the surface. It has been suggested that at least Europa has significant amounts of ocean material expelled into its atmosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months would give valuable insight into many of the processes mentioned above. The LP would measure in-situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby determine the dynamical behaviour of surface weathering and magnetospheric influences. Moreover, LP voltage sweeps would also give information on the Ly-alpha UV intensity and micrometer dust impacts, both important parameters for determining the surface-space interaction processes. By making use of two LP sensors the plasma flow and dc electric field components can be estimated. These are important for determining the detailed dynamics of the interaction of Jupiter's magnetosphere with its moons. The instrument proposed has heritage from the Rosetta LAP instrument, the Cassini RPWS Langmuir Probe, as well as the Cluster EFW plasma wave experiment.