The International Astronomical Union has (finally) come up with a proposal for the definition of a planet: it’s round. If accepted, it means our Solar System has at least 12, not 9, planets.

NEWS Planets are round. Will that do?

EDITORIAL Round objects

Here’s an amusing excerpt from the IAU questions and answers factsheet:

Q: Is a “pluton” a planet?

A: Yes.

….so… that clears that up then.

Do you agree with the definition? Disagree? Let us know.

And do you have a handy mnemonic to remember the new planets by? (That’s Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, UB313/Xena). Here’s one popular one used to remember the more traditional 9 planets: “My Very Educated Mother Just Served Us Nine Pizzas”