For decades, the solar system was formed by nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. However, in August 2006 in Prague, the Czech capital was a meeting of the International Astronomical Union (IAU), which resulted in the recognition of only eight planets, and Pluto is now classified as a “planet dwarf.”
According to the IAU, the entity responsible for the classification of celestial bodies, a planet must present some basic features, such as turning around a major star, have sufficient mass to produce the gravitational force to give it a spherical shape, thus eliminating its orbit other bodies, or be dominant in its orbital zone.
Pluto, which was the ninth planet from the Sun (star of the solar system), was downgraded to a category of “dwarf planet”, including that group along with two other celestial bodies: Ceres and Eris. This decision was motivated by astronomers because Pluto’s orbit affect the orbit of Neptune, and present shape, mass and size quite different from other planets.
Pluto, which was considered a planet in the solar system since 1930, did not fit in some of the requirements for a body that can be classified as a planet. Thus, in 2006, was his demotion to dwarf planet.