Science opportunities with a double Langmuir probe and electric field experiment for JIMO

The three icy Galilean moons of Jupiter: Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. They all have thin atmospheres with residence times of a few days at most. The surface interactions with the space environment determine the atmospheric and ionospheric properties. The Jupiter Icy Moons Orbiter (JIMO) gives possibilities to investigate the weathering properties of their surfaces and volatile material expelled from their interiors. The atmospheres and the ionized ionospheric components of the Galilean moons (including the volcanic moon Io) interact strongly with the co-rotating magnetosphere of Jupiter. This interaction is dynamic and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. The icy moon’s ionospheres are likewise highly variable in time and estimated peak electron densities vary between 1000 and 20,000 cm−3 near their surfaces. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months will give valuable insight into these processes. Foremost the LP measures in situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby provides estimates of key parameters for the dynamical behaviour of surface weathering and magnetospheric influences. In addition many other physical parameters important to the dynamics of these systems can be estimated with such an instrument, like the plasma flow and the DC electric field. Recent results from the LP part of the Radio and Plasma Wave Science (RPWS) on board the Cassini/Huygens spacecraft orbiting Saturn show that an LP works in extended plasma parameter domains with very good science return.