In a couple of the premade spellbooks included in Ultimate Magic, the 5th level Wizard spell comet is included. Here's an example linked from the PRD.
I've checked UM, the core books, a good portion of the splatbooks, searched the PRD and the PFSRD, and even checked in 3.5 material, and I don't see this spell included anywhere. Am I overlooking it? Or was it most likely a spell that was cut but overlooked in the premade spellbook listings?