Every now and then a scientific paper makes a real splash. We had one recently, to judge from recent headlines. “Moon rises to claim its place as a planet” said The Sunday Times on February 19, while the Mail Online asked “Is this lunarcy?”. The articles were among many responding to the humble paper: “A Geophysical Planet Definition”, which suggested that the criteria for determining what constitutes a planet need an overhaul. It argued that the moon, Pluto and several other bodies in the solar system should be upgraded to planets.