1. R. P. Lin, Space Sciences Laboratory and Physics Department, University of California, Berkeley, CA 94720, USA. D. L. Mitchell, D. W. Curtis, K. A. Anderson, C. W. Carlson, J. McFadden, Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA. M. H. Acuña, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. L. L. Hood, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA. A. Binder, Lunar Research Institute, Gilroy, CA 95020, USA.