1. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
2. Department of Geological Sciences, Brown University, Providence, RI 02912, USA.
3. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
4. Smithsonian Institution, Washington, DC 20013, USA.
5. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
6. Faculty of Earth Sciences, China University of Geosciences, Wuhan, Hubei, 430074, P. R. China.
7. School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85251, USA.
8. Institute of Planetary Research, German Aerospace Center, D-12489 Berlin, Germany.