What is the main conflict in Lucifer's Hammer by Larry Niven?

Tim Hamner arrives at a party thrown by Julia and George Sutter to announce that a comet he discovered has been authenticated and named the Hamner-Brown Comet. The "Brown" is a youngster who reported his own sighting about the same time. Tim explains that he found it first but waited for some time to be certain that it really was a comet before making the report.