The International Astronomical Union (IAU) is meeting this week in Prague and 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.
Pluto is already an unusual planet. It is made predominantly of ice, and is smaller even than the Earth's Moon. But its status as the ninth planet could also be in danger if the experts decide it no longer makes the grade. From today's BBC report:
Any decision to downgrade Pluto would send shockwaves through the scientific community, instantly outdate textbooks, and change how the basics of the Solar System are taught in schools.
Since the discovery of the ninth planet, astronomers have become aware of a vast population of small, icy bodies resembling Pluto that orbit the Sun beyond Neptune, in a region called the Kuiper Belt.
This led some astronomers to argue that Pluto belonged with this population of "icy dwarfs", not with the objects we call planets.