1. Department of Planetary Sciences, University of Arizona, Tucson 85721
2. U.S. Geological Survey, Flagstaff, Arizona 86001
3. Department of Astronomy, New Mexico State University, Las Cruces 88003
4. NASA Headquarters, Washington, D.C. 20546
5. Jet Propulsion Laboratory, Pasadena, California 91109
6. Center for Astrophysics, Cambridge, Massachusetts 02138
7. NASA/Ames Research Center, Moffett Field, California 94035
8. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena 91125
9. Rand Corporation, Santa Monica, California 90406
10. University College London, London WC IE 6BT, England
11. Institute for Astronomy, University of Hawaii, Honolulu 96822
12. Department of Earth and Space Sciences, State University of New York, Stony Brook 11790
13. Cornell University, Ithaca, New York 14853
14. Lunar and Planetary Laboratory, University of Arizona, Tucson 85721
15. University of Wisconsin, Madison 53706