1. Department of Earth, Atmospheric, and Planetary Sciences; Purdue University; West Lafayette Indiana USA
2. Department of Physics; Purdue University; West Lafayette Indiana USA
3. Department of Earth, Atmospheric, and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA
4. Solar System Exploration Division; NASA Goddard Space Flight Center; Greenbelt Maryland USA
5. Planetary Science Directorate; Southwest Research Institute; Boulder Colorado USA
6. Lamont-Doherty Earth Observatory; Columbia University; Palisades New York USA
7. Department of Terrestrial Magnetism; Carnegie Institution of Washington; Washington District of Columbia USA
8. Institut de Physique du Globe de Paris, Sorbonne Paris Cité; Université Paris Diderot; Paris CEDEX 13 France