1. Max-Planck-Institute for Solar System Research; Göttingen Germany
2. Rheinisches Institut fuer Umweltforschung, Abteilung Planetforschung; Cologne Germany
3. Department of Physics and Astronomy; University of Iowa; Iowa City IA USA
4. Space Sciences Laboratory; University of California; Berkeley CA USA
5. NASA Goddard Space Flight Center; Greenbelt MD USA
6. Laboratory for Atmospheric and Space Physics; University of Colorado Boulder; Boulder CO USA
7. Institute of Space Research; Moscow Russia