1. National Optical Astronomy Observatories, Tucson, AZ 85719, USA.
2. Department of Geology, Arizona State University, Tempe, AZ 85287-1404, USA.
3. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 87721, USA.
4. U.S. Geological Survey, Flagstaff, AZ 86001, USA.
5. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
6. Department of Geology, Brown University, Providence, RI 02912, USA.
7. Deutsche Forschungsanstalt fur Luft und Raumfahrt, 8031 Oberpfaffenhofen, Federal Republic of Germany
8. Planetary Science Institute, Tucson, AZ 85719, USA.
9. Institute for Space and Terrestrial Science, Concord, Ontario, Canada L4K 3C8.
10. U.S. Geological Survey, Menlo Park, CA 94025, USA.
11. RAND, Santa Monica, CA 90406, USA.
12. Institute of Geophysics, University of Hawaii, Honolulu, HI 96822, USA.
13. Department of Astronomy, Cornell University, Ithaca, NY 14853, USA.
14. California Institute of Technology, Pasadena, CA 91125, USA.
15. NASA Headquarters, Washington, DC 20546, USA.