1. Department of Geology and Geophysics; Yale University; New Haven CT USA
2. UK Centre for Astrobiology, School of Physics and Astronomy; University of Edinburgh; Edinburgh UK
3. Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge MA USA
4. Division of Geological and Planetary Sciences; California Institute of Technology; Pasadena CA USA
5. Department of Earth, Environmental and Planetary Sciences; Brown University; Providence RI USA
6. Jet Propulsion Laboratory; California Institute of Technology; Pasadena CA USA