1. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109
2. Physics Department, York University, 4700 Keele Street, North York, Ontario, M3J IP3, Canada
3. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139
4. National Aeronautics and Space Administration, Washington, DC 20546
5. TRW, 1 Space Park, Redondo Beach, CA 90278
6. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822