1. Solar System Exploration Division, NASA Goddard Space Flight Center; Greenbelt; Maryland; USA
2. Department of Physics and Astronomy; University of Iowa; Iowa City; Iowa; USA
3. Space Science and Applications, Los Alamos National Laboratory; Los Alamos; New Mexico; USA
4. Swedish Institute of Space Physics; Uppsala; Sweden
5. Department of Material Science and Engineering; University of Virginia; Charlottesville; Virginia; USA
6. Space Science and Engineering, Southwest Research Institute; San Antonio; Texas; USA