xkcd: Possible Undiscovered Planets

Randall Munroe is a genius at disguising seriously educational infographics as funny jokes. Behold today's xkcd: "Possible Undiscovered Planets," a reference, of course, to yesterday's announcement of theoretical evidence for a possible, distant ninth planet. Visit the xkcd site to enjoy the mouseover text (use this link if you're on a mouseless device).