Donald K. Yeomans is a fellow and senior research scientist at the Jet Propulsion Laboratory, where he is manager of NASA's Near-Earth Object Program Office and supervisor of the Solar System Dynamics Group. He is the author of "Comets: A Chronological History of Observation, Science, Myth, and Folklore."Melinda D. Merck, DVM, is a forensic veterinarian with the ASPCA(R) (The American Society for the Prevention of Cruelty to Animals(R)), and frequently provides training for veterinary and law enforcement professionals nationwide on the use of veterinary medical knowledge in the investigation and prosecution of animal cruelty cases. In addition, she is a veterinary forensics consultant for the Fulton County District Attorney's Office in Atlanta, Ga., and also conducts veterinary forensic examinations for Gwinnett County Animal Control. Dr. Merck often testifies as a forensic veterinary expert for animal cruelty cases around the country, including cases involving animal hoarding, dog fighting and animal torture. She has previously worked as an associate veterinarian in both private practice and animal hospital settings.