1. Department of Physics and Astronomy; University College London; London UK
2. Centre for Planetary Sciences at UCL/Birkbeck; London UK
3. Physics Department; Lancaster University; Lancaster UK
4. Office of Space Research and Technology, Academy of Athens; Athens Greece
5. Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens; Athens Greece
6. Space and Atmospheric Physics Group, Blackett Laboratory, Imperial College London; London UK