When Pluto was first discovered, it was considered to be the 9th planet in our Solar System. But as telescopes grew more powerful astronomers discovered more objects that lie near Pluto and even rival its size. This was fuelled when Eris, a body that was bigger than Pluto, was discovered.
In 2006, after much discussion, Pluto was stripped of its status as a planet. The scientists agreed that for a celestial body to qualify as a planet:
- it must be in orbit around the Sun,
- it must be large enough that it takes on a nearly round shape,
- it has cleared its orbit of other objects.
Pluto, Eris and several other bodies became classed a new breed of planets: dwarf planets.
There are currently 5 known dwarf planets: Ceres, Pluto, Makemake, Haumea and Eris. Apart from Ceres, they all orbit beyond Neptune and come under a class called Plutoids.
It is predicted that in the Kuiper Belt, there could be hundreds of dwarf planets just waiting to be discovered!