The International Astronomical Union has been meeting in Prague over the past week to determine, among other things, what is and what is not a planet. Today the assembled astronomers voted and the official definition is now "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."
What this means is that Pluto is out. It is automatically disqualified because its orbit crosses that of Neptune. This also means that Gustav Holst had it pegged when his Suite for Large Orchestra, "The Planets" ended with Neptune. Since Pluto is now officially a "dwarf planet" (new designation) that also means that its name has been changed to Sneezy.