* Pluto was once considered the ninth planet but was reclassified as a dwarf planet in 2006.

* The International Astronomical Union (IAU) defined a planet as an object that orbits the Sun, has enough mass to be round due to its own gravity, and has cleared its neighborhood around its orbit. Pluto doesn't meet this last criteria.

Therefore, our solar system currently consists of eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.