For a long time, kids learned about the nine planets in our solar system, and Pluto was one of them. But in 2006, something big happened that changed everything: Pluto was no longer called a planet. Let’s find out why this happened and what makes something a planet.
Pluto was found in 1930 by a scientist named Clyde Tombaugh. It was known as the smallest planet in our solar system, along with the other eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
In August 2006, scientists met in Paris at a group called the International Astronomical Union (IAU) and decided that Pluto should not be called a planet anymore. This meant schools had to change their books, and people started asking what makes something a planet.
The IAU says that to be a planet, a space object must do three things:
1. **Revolves Around the Sun**: It must travel around the Sun.
2. **Spherical Shape**: It must be round because of its gravity.
3. **Clears Its Orbit**: It must have enough gravity to push away other space rocks and objects around it.
Pluto does the first two things but not the third one. It hasn’t cleared its path of other objects, so it’s now called a dwarf planet.
Pluto isn’t the only dwarf planet. It’s part of a group of space objects in an area called the Kuiper Belt, which is beyond Neptune. Other dwarf planets like Haumea and Makemake are there too. There’s also Eris, which is even bigger than Pluto!
To help everyone understand what makes a planet, the IAU made a checklist. Pluto and other dwarf planets do the first two things on the list but not the third, so they are called dwarf planets.
– An 11-year-old girl named Venetia Burney suggested the name “Pluto” in 1930.
– Pluto has ice volcanoes and might have a hidden ocean under its icy surface!
Pluto’s change from a planet to a dwarf planet made people talk and wonder. Knowing what makes a planet helps us understand why Pluto’s status changed. As we learn more about space, the way we classify planets might change, but Pluto will always be an exciting topic to learn about!
Planetary Model Creation: Gather some clay or playdough and create models of the planets in our solar system, including Pluto. As you make each planet, think about the three criteria that the IAU uses to define a planet. Discuss with a friend or family member why Pluto doesn’t meet all the criteria. Can you identify which planets meet all three criteria?
Orbit Observation: Use a flashlight to represent the Sun and small balls or marbles to represent the planets. Create a model of the solar system on a table or the floor. Move the planets around the “Sun” to see how they orbit. Notice how Pluto’s path might be different from the other planets. Discuss why it’s important for a planet to clear its orbit and what that means for Pluto.
Question Time: Think about these questions and discuss them with your class or family:
