Finally, astronomers could be homing in on a definition of the word planet. After a day of public bickering in Prague, followed by negotiations behind closed doors, the latest draft resolution was greeted with a broadly friendly reception.Previously:
If accepted on Thursday, it would be bad news for Pluto, which would no longer be a full-fledged planet.
The crucial change in "draft c" is that a planet must be the dominant body in its orbital zone, clearing out any little neighbours. Pluto does not qualify because its orbit crosses that of the vastly larger Neptune.
Planet doesn't need a scientific definition
Pluto may yet lose planet status
IAU planet definition Q&A sheet
And soon, there will be twelve planets