1. Astronomy Department, University of Washington, Seattle, Washington, USA.
2. NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA.
3. Astrobiology Program, University of Washington, Seattle, Washington, USA.
4. Now at: NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
5. Now at: NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland, USA.
6. NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.
7. Department of Atmospheric and Oceanic Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, Colorado, USA.
8. Now at: University of California at Riverside, Riverside, California, USA.
9. Now at: Paris-Meudon Observatory, Paris, France.
10. Blue Marble Institute of Science, Seattle, Washington, USA.
11. Department of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK.
12. University of Exeter, Exeter, Devon, UK.