What Makes a Planet a Planet?

To understand why some objects in space are called planets and others are called dwarf planets, we need to learn about what makes a planet special. There are three main rules that an object in space must follow to be considered a planet:

1. It orbits a star: A planet must travel around a star, like our Sun.
2. It is round: A planet needs to be big enough that its own gravity pulls it into a round shape.
3. It has cleared its orbit: A planet must be the biggest thing in its orbit. This means it should have pushed away or absorbed other objects in the path where it travels around the star.

What is a Dwarf Planet?

A dwarf planet is similar to a planet, but it doesn't meet all the rules above. Specifically, it does not clear its orbit of other objects. This means there are still other big rocks or ice in its orbital path.

Why is Pluto No Longer Considered a Planet?

Pluto used to be considered the ninth planet from the Sun. However, in 2006, scientists changed its classification. Here’s why:

1. Pluto does orbit the Sun and is round, so it fits the first two rules about being a planet.
2. But, Pluto does not meet the third rule because it shares its orbit with many other objects in a region called the Kuiper Belt.

Since Pluto could not clear its orbit of other objects, astronomers decided to classify it as a dwarf planet instead of a planet. So now Pluto is a part of a special group of objects that are called dwarf planets.

In summary, a planet must orbit a star, be round, and be big enough to clear other objects in its path. Pluto is not currently considered a planet because it shares its space with other similar objects.