Pluto is a dwarf planet beyond the orbit of Neptune. It was discovered in 1930, the first space object in the Kuiper belt. It was instantly called the 9th planet of the Solar system. Later, five moons were discovered orbiting Pluto. Then Pluto’s planetary status was doubted when it was found to be much smaller than expected. As a result, in 2006, the International Astronomical Union formally reconsidered the term planet to exclude dwarf planets such as Pluto.