what if Earth and Mars switched places?

Why isn't Pluto a major planet?

That's a great question!

if we think of all the planets

in our solar system as being like one big family,

then removing Pluto from the list of planets

might kind of feel like we're kicking it out of our family.

Poor Pluto.

So, why are scientists saying we shouldn't think of Pluto

as one of the major planets of our solar system?

Well, if you want to figure out the answer to this question,

it's helpful to know about a true story,

a story not about Pluto,

but about a different planet in our solar system.

This, the planet Ceres.

I know what you might be thinking.

Ceres?

Doug, I've never heard of Ceres.

Are you sure that's a real planet?

But I promise you, I'm not making this up.

You see, it all starts about 200 years ago.

Back then, any child learning about the planets

learned most of the same planets you learn about.

In school, all learn the names of Mercury, Venus,

Earth, Mars, Jupiter, Saturn, Uranus,

until one day, in the year 1800, an astronomer,

a scientist who studies space was carefully looking

through their telescope and discovered a new planet.

It was a tiny, little planet

located in between the planets, Mars and Jupiter.

The whole world was pretty amazed.

Wow, a new planet?

That's exciting.

It was decided to name this little planet, Ceres,

and so, Ceres got added to the list of planets

everyone learned, Mercury, Venus, Earth,

Mars, Ceres, Jupiter, Saturn, and so on.

Cool, but it gets better.

Because you see, the very next year,

a different astronomer found another new planet.

This one was also located in between the planets,

Mars and Jupiter, not too far from Ceres actually.

Wow, and it was also kind of little.

It was decided to name this little planet, Pallas.

And so, children in school learned the names of the planets,

Mercury, Venus, Earth, Mars, Ceres,

Pallas, Jupiter, Saturn, and so on.

But wait, because, just a few years later,

that same astronomer found yet another small planet

and, again, this one

in between the planets, Mars and Jupiter,

not too far from our new friends, Ceres and Pallas.

It was decided to name this planet, Vesta.

Now, by this point, you can see,

if you were learning the names of the planets,

that's getting to be a pretty long list.

And it kept getting harder and harder to learn

because of guess what, just a few years later,

another little planet was discovered,

and another, then another.

Soon, there were thousands of these little planets

being found between Mars and Jupiter.

Astronomers realized that, with these little tiny planets

that kept getting discovered,

they were dealing with something new, something unusual.

Do you know what all these little, tiny planets are?

Well, all these tiny little planets

found between the planets of Mars and Jupiter

got their own special name.

Maybe you've heard of them before, asteroids.

We know today that asteroids

are basically giant rocks floating around in space?

They are similar to planets in some ways,

but they're also much smaller than the other planets,

and there's so many of them.

Rather than learn all of their names,

we simply call this whole area

in between Mars and Jupiter, the asteroid belt

since, when you make a map of it,

its kind of looks like the shape of a belt

going around the sun.

So that's the story,

but what does all this have to do with Pluto?

Well, you see, many years later,

when Pluto was first discovered,

it was the farthest planet we'd ever discovered,

way, way out at the very far end of the solar system.

But, starting in the 1990s, astronomers

had better telescopes and cameras than ever before.

In the year 1992, they discovered a new planet

out by Pluto, the planet Albion.

Then, just a few years later, another one,

and then another one, and another one and another.

Today, they found thousands of little, tiny planets,

similar to Pluto, all of them out there

at the very far end of our solar system.

You see the similarities to the earlier story?

What astronomers have realized

is that there's another belt in our solar system.

This one isn't between Mars and Jupiter.

It's a belt that's out at the very far end

of our solar system, a belt they've named the Kuiper Belt,

in honor of Gerard Kuiper,

an astronomer who predicted that this belt might exist.

So, now, you can finally start to see why scientists

are saying, it makes sense to think of Pluto

as something different than one of the major planets.

Just like Ceres, Pluto turns out to be

part of a belt of small, tiny planets.

When you think of our family of planets,

it's still okay if you include Pluto.

It is still a planet, That's all for this question.