1. Solar System Exploration Division; NASA Goddard Space Flight Center; Greenbelt Maryland USA
2. Department of Astronomy; University of Maryland; College Park Maryland USA
3. Laboratory for Atmospheric and Space Physics; University of Colorado Boulder; Boulder Colorado USA
4. Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
5. Space Sciences Laboratory; University of California; Berkeley California USA
6. Institute for Astrophysics and Computational Sciences; Catholic University of America; Washington District of Columbia USA
7. CNRS, Institut de Recherche en Astrophysique et Planétologie; Toulouse France
8. Paul Sabatier University; Toulouse France