The Europa Charging Environment

The baseline design of the planned Europa Mission includes large solar arrays, which may experience surface charging. The spacecraft would encounter Europa ~40 times with some passes within ~25 km. This paper will describe the plasma environment expected near Europa during these encounters. Emphasis will be on the torus near Europa and on Europa's ionosphere. Whereas the spacecraft would encounter a cold, corotating torus plasma with a velocity of ~120 km/s near Europa, it may encounter Europa's ionosphere at a velocity as low as 5 km/s as Europa's orbital velocity is only ~14 km/s relative to Jupiter. The challenge is to estimate the rapid potential variations associated with these two disparate environments. This paper will present a review of models of the plasma torus and the ionosphere and their interactions with each other. Ultimately, the models will be used to estimate the effects of the varying plasmas near Europa on the planned Europa Mission's baseline spacecraft design and on its instruments with the intent of hardening that design to surface charging and to help with the interpretation of the effects of the charging environment on its instruments.