Theodore P. Snow is professor emeritus at the Center for Astrophysics and Space Astronomy at the University of Colorado Boulder. Over the course of his career, he has worked on two orbital telescopes, including the Hubble Space Telescope, built experiments for rocket and satellite observations, and studied chemical reactions important in interstellar space. He is the author of the award-winning textbook The Dynamic Universe. Don Brownlee is professor emeritus of astronomy at the University of Washington. He has been involved in spacecraft, rocket, high-altitude balloon, and U-2 airplane experiments since he was a graduate student, and he was the principal investigator in charge of the NASA Stardust mission that collected samples from a comet and returned them to Earth. He is the coauthor of Rare Earth and Life and Death of Planet Earth.