There are all sorts of rules for naming celestial bodies and other features out there. In the case of craters on planets and moons, the International Astronomical Union requires that they be named after “deceased artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field and have been recognized as art historically significant figures for more than 50 years.”
With the MESSENGER probe’s new survey of Mercury complete, it was time to give names to a long list of geological features. In addition to John Lennon, craters now bear names like Caruso (Enrico Caruso, the opera star) and Berlioz (composer Hector Berlioz). More on the story at NBC News.