1. Exobiology Branch, MS239-4, NASA Ames Research Center, Moffett Field, California94035, United States
2. SETI Institute, 189 Bernardo Avenue, Suite 200, Mountain View, California94043, United States
3. Exobiology Branch, MS239-4, NASA Ames Research Center, Moffett Field, California94033, United States
4. Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California94132, United States