1. Department of Astronomy, University of Washington, Seattle, WA 98195, USA, E-mail: brownlee@uw.edu
2. Space Science Institute, Boulder, CO 80301, USA, E-mail: bclark@spacescience.org
3. Department of Astronomy, University of Maryland, College Park, MD 20742, USA, E-mail: jess@astro.umd.edu
4. *published posthumously
5. Department of Earth Science, Tohoku University, Sendai 980-8578, Japan, E-mail: tomoki@m.tohoku.ac.jp