Nov. 18, 2010 at 8:35 PM ETBrian Marsden, an expert on comets and longtime head of the Minor Planet Center, passed away today at the age of 73. Marsden was kind enough to help me get an asteroid named for "Hitchhiker" humorist Douglas Adams, and was also generous with his time and his expertise while I was working on my book, "The Case for Pluto." He didn't agree with me on Pluto, but he was always agreeable. I hope that comes through in my book. His name lives on -- and I don't just mean that figuratively. The asteroid 1877 Marsden will still be circling the sun long after all of us are dust.