At its conference this August, the International Astronomical Union (IAU) will make a decision that could see Pluto lose its status as a planet.
For the first time, the organisation will be officially defining the word "planet", and it is causing much debate in the world of astronomy.
There is only one thing that everyone seems to agree on: there are no longer nine planets in the Solar System.
Matters were brought to a head by the discovery in January of last year of a potential 10th planet, temporarily named 2003 UB313.
Professor Mike Brown and his team at the California Institute of Technology have already discovered several large objects on the edge of the Solar System, but 2003 UB313 is special because it is bigger than Pluto.
The question now facing the IAU is whether to make this new discovery a planet.
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