[1] US GEOL SURVEY, FLAGSTAFF, AZ 86001 USA
[2] NEW MEXICO STATE UNIV, DEPT ASTRON, LAS CRUCES, NM 88003 USA
[3] NASA, HEADQUARTERS, WASHINGTON, DC 20546 USA
[4] JET PROP LAB, PASADENA, CA 91109 USA
[5] CTR ASTROPHYS, CAMBRIDGE, MA 02138 USA
[6] NASA, AMES RES CTR, MOFFETT FIELD, CA 94035 USA
[7] CALTECH, DIV GEOL & PLANETARY SCI, PASADENA, CA 91125 USA
[8] RAND CORP, SANTA MONICA, CA 90406 USA
[9] UNIV LONDON UNIV COLL, LONDON WC1E 6BT, ENGLAND
[10] UNIV HAWAII, INST ASTRON, HONOLULU, HI 96822 USA
[11] SUNY STONY BROOK, DEPT EARTH & SPACE SCI, STONY BROOK, NY 11790 USA
[12] CORNELL UNIV, ITHACA, NY 14853 USA
[13] UNIV ARIZONA, LUNAR PLANETARY LAB, TUCSON, AZ 85721 USA
[14] UNIV WISCONSIN, MADISON, WI 53706 USA