Most grown-ups learned about Pluto in school, and even scientists used to call Pluto a planet. But people have always known that Pluto was different from the big planets. Here you can find out what a planet is, why scientists finally decided that Pluto isn’t really a planet after all, and lots of other interesting facts!
We live on Earth. Earth is a planet. Looking up in the sky, you can see the sun, the moon, and probably the stars. Some of the stars you see are actually planets like Earth, but they're so far away that they just look like tiny dots of light up in the sky.
It might seem like the sun and moon and other things up in the sky go around the Earth. The moon does go around the Earth, but Earth and the other planets go around the sun. The sun and all the planets that go around it are called the solar system.
There are other things that go around the sun, too, like asteroids and comets. Asteroids are like big lumpy rocks in space, and comets are kind of like big lumpy space snowballs. There are even little mini planets that are round like the big planets but are different from the big planets. The most famous of these mini planets is Pluto.
Lots of people still call Pluto a planet. They think Pluto is just like Earth and the other big planets. But Pluto is a lot more like all the little mini planets in the solar system. Scientists decided that Pluto and these other little mini planets need their own special name. Now they are called dwarf planets.