Pluto, called a planet for seventy-five years, is now dead, banished to the lowly status of "dwarf planet.". While astronomers argued about Pluto for most of the past decade, the final death blow came with the discovery of Eris -- an even larger body in the outer solar system. I'll discuss the story of the search for and the discovery of Eris and try to give a perspective on why the question of planethood for Pluto and for Eris matters and why, in the end, astronomers made the right decision to demote Pluto.

Dr. Michael E. Brown is a professor of planetary astronomy at the California Institute of Technology and has been on the faculty there since 1996.

He specializes in the discovery and study of bodies at the edge of the solar system. Among his numerous scientific accomplishments, he is best known for his discovery of Eris, the largest object found in the solar system in 150 years, and the object which led to the debate and eventual demotion of Pluto from a real planet to a dwarf planet.

He has authored nearly 100 scientific papers, and his writing has appeared in such venues as the New York Times, Physics Today, and the World Book Science Year.

Dr. Brown received his AB from Princeton, MA and PhD from University of California, Berkeley. He has won several awards and honors for his scholarship, including the prestigious Urey Prize for best young planetary scientist from the American Astronomical Society's Division of Planetary Sciences; a Presidential Early Career Award; a Sloan Fellowship; and, of course, the one that started his career, an honorable mention in his fifth-grade science fair. He was also named one of Wired Online's Top Ten Sexiest Geeks in 2006, the mention of which never ceases to make his wife laugh.