1. 1Department of Earth and Planetary Sciences, Stanford University, Stanford, California 94305, USA
2. 2School of Earth, Atmosphere & Environment, Monash University, Clayton, VIC 3800, Australia
3. 3Department of Earth, Planetary, and Space Sciences, University of California–Los Angeles, Los Angeles, California 90095, USA
4. 4Department of Space Studies, Southwest Research Institute, Boulder, Colorado 80302, USA