For more information - BBC NewsAbout 2,500 scientists meeting in Prague have adopted historic new guidelines that see the small, distant world demoted to a secondary category.
The researchers said Pluto failed to dominate its orbit around the Sun in the same way as the other planets.
The International Astronomical Union's (IAU) decision means textbooks will now have to describe a Solar System with just eight major planetary bodies.
Personally I'm amazed at this decision! It'll be so difficult to appreciate a solar system with just eight planets. How do you think Pluto will feel about it?