Wow: No sooner did the media herald the discovery of a "new Planet" that astronomers began to question whether it should be called a planet at all. Along with Pluto, it looks like both are in for a sharp degrade of status from Planet to mere planetisimal. Is this right ? Or should we seriously rethink the parameters we use to call something a planetisimal. If this is the case for Pluto and Sedna, why not Mercury? After all, Mercury is only slightly larger than our own moon and Ganymede is certainly much bigger than Mercury, but isn't considered a planet. So what is the most clear and sustainable definition of " Planet " ? given these contradictory size examples ?