CHRISTOPHER CHYBA is professor of astrophysical sciences and international affairs at Princeton University, where he directs the Program on Science and Global Security at the Woodrow Wilson School. His work in international security emphasizes nuclear and biological weapons policy, arms control, and nonproliferation. His scientific research focuses on solar system physics, planetary exploration, and astrobiology. Dr. Chyba has co-directed Stanford University’s Center for International Security and Cooperation, held the Carl Sagan Chair for the Study of Life in the Universe at the SETI Institute, served on the White House staff from 1993 to 1995. Dr. Chyba received the Presidential Early Career Award was named a MacArthur Fellow for his work in both international security and planetary science. Dr. Chyba has served on the executive committee of NASA’s Space Science Advisory Committee. President Obama appointed Dr. Chyba as a member of the President’s Council of Advisors on Science and Technology.