[1] Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA
[2] Univ Calif Berkeley, Dept Astron, 601 Campbell Hall, Berkeley, CA 94720 USA
[3] NASA, Goddard Space Flight Ctr, Solar Syst Explorat Div 690 0, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA
[4] CALTECH, Jet Prop Lab, M-S 183-501,4800 Oak Grove Dr, Pasadena, CA 91109 USA
[5] British Astron Assoc, Burlington House, London W1J 0DU, England
[6] Univ Michigan, Dept Climate & Space Sci & Engn, Space Res Bldg,2455 Hayward St, Ann Arbor, MI 48109 USA
[7] New Mexico Inst Min & Technol, Dept Phys, Workman Ctr 345, 801 Leroy Pl, Socorro, NM 87801 USA
[8] Space Telescope Sci Inst, 3700 San Martin Dr, Baltimore, MD 21218 USA
[9] Univ Calif Berkeley, Dept Mech Engn, Berkeley, CA 94720 USA