[1] Univ Utah, Dept Geol & Geophys, Salt Lake City, UT 84112 USA
[2] CSIC INTA, Ctr Astrobiol, Madrid, Spain
[3] Johns Hopkins Univ, Appl Phys Lab, Laurel, MD 20723 USA
[4] US Geol Survey, Flagstaff, AZ 86001 USA
[5] Univ G dAnnunzio, Int Res Sch Planetary Sci, I-65127 Pescara, Italy
[6] Cornell Univ, Dept Astron, Ithaca, NY 14853 USA
[7] Washington Univ, Dept Earth & Planetary Sci, McDonnell Ctr Space Sci, St Louis, MO 63130 USA
[8] Univ Arizona, Lunar & Planetary Lab, Tucson, AZ 85721 USA