1. Department of Physics and Astronomy; University of Southampton; Southampton UK
2. Planetary Science Institute; Tucson AZ USA
3. Office of Space Research and Technology; Academy of Athens; Athens Greece
4. Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing; National Observatory of Athens; Athens Greece
5. Applied Physics Laboratory; The Johns Hopkins University; Laurel MD USA
6. Max-Planck-Institut für Sonnensystemforschung; Goettingen Germany