Listen to an interview via RealAudio with the author of "Planet Quest," and also find a bibliography of Croswell's works.

Follow an interview with David Levy, author of the book "Comets: Creators and Destroyers."

Check out the first chapter of Posner's book "Aging and Old Age."

Read the first chapter of Ryan's book "Virus X" about tracking the evolution of plagues.

Find an interview and biography of the author of "Stealing Time: The New Science of Aging," which explores the science behind longer lives.