1. Department of Planetary Sciences, University of Arizona, Tucson 85721
2. U.S. Geological Survey, Flagstaff, Arizona 86001
3. Jet Propulsion Laboratory, Pasadena, California 91103
4. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena 91125
5. Jet Propulsion Laboratory
6. U.S. Geological Survey, Flagstaff
7. University College London, London WC IE 6BT, England
8. U.S. Geological Survey, Menlo Park, California 94025
9. Rand Corporation, Santa Monica, California 90406
10. Smithsonian Astrophysical Observatory, Cambridge, Massachusetts 02138
11. California Institute of Technology
12. Department of Earth and Space Sciences, State University of New York, Stony Brook 11790
13. Cornell University, Ithaca, New York 14853
14. Department of Astronomy, New Mexico State University, Las Cruces 88003
15. Cornell University
16. Lunar and Planetary Laboratory, University of Arizona
17. Institute for Astronomy, University of Hawaii, Honolulu 96822
18. NASA Headquarters, Washington, D.C. 20546
19. Space Science and Engineering Center, University of Wisconsin, Madison 53706