Why Isn't Pluto a Planet Anymore? — For Kids

Why Isn't Pluto a Planet Anymore? — Elementary

The short answer

In 2006, Pluto changed groups.

It was a planet.

Now it is a dwarf planet.

Why did Pluto change?

Pluto was the ninth planet.

It was the smallest planet.

Astronomers found more objects.

The new objects are small, like Pluto.

They are Ceres, Makemake, Haumea, and Eris.

All of them are much smaller than the other planets.

So astronomers made a new family.

The new family is called dwarf planets.

Pluto is in that family now.

Pluto's home

Pluto is in the Kuiper Belt.

The Kuiper Belt is a wide ring.

It is made of icy bodies.

It is just outside Neptune's orbit.

Pluto is the largest object there.

Pluto is called the King of the Kuiper Belt.

The belt has bits of rock and ice.

It has comets and dwarf planets, too.

It is named for Gerard Kuiper.

In 1951, he said a belt like this might be there.

He wanted to explain comets with small orbits.

What about Eris?

From the “All About Pluto” page: Eris may be as big as Pluto. It may be a little bigger than Pluto.

From the “What Is the Kuiper Belt?” page: Eris is a little smaller than Pluto, but it has more mass. It takes 557 years to orbit the Sun.

Fun facts about Pluto

Pluto is about half the width of the United States.

Pluto has a moon named Charon.

Charon is about half the size of Pluto.

Charon is the largest moon compared to the body it orbits.

Pluto's orbit is oval. It is tilted, too.

For part of its orbit, Pluto is closer to the Sun than Neptune. That part is about 8% of its orbit.

One year on Pluto is 248 Earth years.

Charon orbits Pluto in about 6.5 Earth days.

One day on Pluto takes the same time.

So Charon hovers over the same spot on Pluto.

Pluto is very cold. Its surface is about 400 degrees below zero Fahrenheit.

If you weigh 100 pounds on Earth, you would weigh 7 pounds on Pluto.

Haumea is shaped like a football. It is about 1,200 miles (1,931 km) long.

A trip to Pluto

On January 19, 2006, NASA launched a robot spacecraft.

Its name is New Horizons.

On July 14, 2015, it flew by Pluto.

In early 2019, it flew past Arrokoth.

Arrokoth is a billion miles past Pluto.

It is the farthest world ever studied up close.

Why Isn't Pluto a Planet Anymore? — Middle

The short answer

In 2006, Pluto was reclassified from a planet to a dwarf planet. Pluto is now categorized as a dwarf planet along with other objects in the solar system that are similar to Pluto: Ceres, Makemake, Haumea, and Eris.

Why Pluto is not a planet anymore

A while back, Pluto was the ninth planet from the Sun. It was also the smallest planet.

Astronomers have already named four other objects in the solar system that are about the same small size as Pluto. They are Ceres, Makemake, Haumea, and Eris. Overall, these objects, along with Pluto, are much smaller than the “other” planets.

Astronomers have put these objects into a new family called dwarf planets.

Ceres orbits in the asteroid belt between Mars and Jupiter. Makemake, like Pluto, is part of the Kuiper Belt. Eris' orbit is even farther out.

Pluto and the Kuiper Belt

Pluto is a dwarf planet that lies in the Kuiper Belt. It is an area full of icy bodies and other dwarf planets at the edge of our solar system. Pluto is known as the “King of the Kuiper Belt” — and it is the largest object in the region.

The Kuiper Belt is a wide ring of icy bodies just outside of Neptune's orbit. There are bits of rock and ice, comets, and dwarf planets out there.

The Kuiper Belt is named after a scientist named Gerard Kuiper. In 1951 he had the idea that a belt of icy bodies might have existed beyond Neptune when the solar system formed. He was trying to explain where comets with small orbits came from.

Another interesting Kuiper Belt Object is Haumea. It is shaped like a squashed American football about 1,200 miles (1,931 km) long.

What about Eris?

From the “All About Pluto” page: Eris may be as big as, or even slightly bigger, than Pluto.

From the “What Is the Kuiper Belt?” page: Eris is a Kuiper Belt Object that is a little smaller than Pluto but has more mass. It is so far away it takes 557 years to orbit the Sun.

More facts about Pluto

Pluto is only about half the width of the United States. Charon is about half the size of Pluto. Charon is the largest moon compared to the body it orbits, whether planet or dwarf planet, of any moon in the solar system.

Almost all the planets in our solar system travel around the Sun in nearly perfect circles. But Pluto does not. It takes an oval-shaped path with the Sun nowhere near its center, and its path is quite tilted. Pluto is actually closer to the Sun than Neptune for about 8% of its orbit.

If you lived on Pluto, you would have to live 248 Earth years to celebrate your first birthday in Pluto-years.

If you lived on Pluto, you would see Charon from only one side of the planet. Charon's orbit around Pluto takes about 6.5 Earth days. Pluto's day, one complete rotation, takes exactly the same amount of time. That means Charon always “hovers” over the same spot on Pluto's surface.

At Pluto's current distance from the Sun, the temperature on its surface is about 400 degrees below zero Fahrenheit.

If you weigh 100 pounds on Earth, you would weigh only 7 pounds on Pluto.

A visit to Pluto and past it

On January 19, 2006, NASA launched a robot spacecraft on the long journey. This mission is called New Horizons. New Horizons flew by Pluto and its moons on July 14, 2015.

In early 2019, New Horizons flew past its second major science target — Arrokoth, the most distant object ever explored up close.

A billion miles past Pluto there is an object named Arrokoth. Arrokoth is the farthest world ever studied up close by a spacecraft.