Pluto is not considered a planet by the International Astronomical Union (IAU) due to its redefinition of the term "planet" in 2006. Prior to that, Pluto had been classified as the ninth planet in our solar system since its discovery in 1930. However, the redefinition introduced specific criteria that a celestial body must meet to be classified as a planet.
According to the IAU definition, a planet must:
- Orbit the Sun.
- Be spherical in shape, which is achieved by its own gravity.
- Clear its orbit of other debris or objects.
Pluto satisfies the first two criteria, but it fails to meet the third requirement. Its orbit overlaps with that of Neptune, and it shares its region of space with other small celestial bodies known as Trans-Neptunian Objects (TNOs). Therefore, based on the IAU definition, Pluto is categorized as a "dwarf planet."
The other planets in our solar system, in order of their distance from the Sun, are:
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
These eight planets are commonly referred to as the "classical planets" to distinguish them from other celestial objects like Pluto.