1. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
2. Computer Sciences Corporation, Lanham-Seabrook, MD 20706, USA.
3. Department of Geological Sciences, Case Western Reserve University, Cleveland, OH 44106, USA.
4. National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA.
5. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
6. Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, HI 98622, USA.
7. Department of Earth and Planetary Science, American Museum of Natural History, New York, NY 10024, USA.
8. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
9. Physics Department, The Catholic University of America, Washington, DC 20064, USA.