1. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. Department of Earth Sciences, University of Cambridge, Cambridge CB2 1TN, UK.
3. Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA.
4. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
5. Southwest Research Institute and NASA Solar System Exploration Research Virtual Institute–Institute for the Science of Exploration Targets, Boulder, CO 80302, USA.