Réponse:
In 1930, an astronomer named Clyde Tombaugh discovered Pluto. It was known as the ninth planet in our solar system for a long time until the early 2000s.
In the early 2000s, astronomers found other small objects in the outer solar system, some similar in size to Pluto. This caused a debate about whether Pluto should still be called a planet. In 2006, the International Astronomical Union changed the rules for what makes a planet (size, orbit, shape etc.). Pluto didn't meet these new rules because of its orbit and shape : it had to share its orbit with other objects in the Kuiper Belt.
Pluto is now called a "dwarf planet" like other objects in the outer solar system. This decision was controversial and some people and scientists were disappointed about it.
