Kuiper belt

cold, and far away from Earth. It is also possible that the IAU will change their definition of what constitutes a planet in the future.

In August 2006, the IAU reclassified a number of objects in the solar system as 'dwarf planets', but then decided on a new category of 'plutoid' for the larger TNOs. Currently three plutoids are recognised by the IAU: Pluto, Makemake and Eris. Several other objects in the Kuiper belt are under consideration, with as many as 50 that could eventually qualify. Plutoids and dwarf planets share a number of characteristics with normal planets, but they are not dominant in their orbit around the Sun. The plutoids and dwarf planets classified so far are members of larger populations. For example, the dwarf planet Ceres is the largest body in the asteroid belt, the plutoid Pluto is the largest body in the Kuiper belt, and the plutoid Eris is a member of the scattered disc.

Under the 2008 IAU definition of planet, there are currently eight planets, one dwarf planet, and three plutoids in the solar system. There has been some criticism of the new definition, and some astronomers have even stated that they will not use it. Part of the dispute centres around the idea that plutoids and dwarf planets should be classified as normal planets. For now, the reclassification of Ceres, Pluto and Eris has attracted much media and public attention.

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