Why Is There No Air in Space?

Let's start with space itself.

Space is almost completely empty, and scientists have a name for that, a vacuum.

Like

our vacuum cleaner? Did somebody vacuum up space? Same word, different meaning.

In science, a vacuum is a place with almost nothing in it, not even air, and nobody had to clean it.

Space is so unbelievably huge that its gas is spread super thin.

In deep space, a box the size of a sugar cube might hold just a few tiny bits of gas.

And how many bits are in a sugar cube of our air? About 25 quintillion.

That's 25 with 18 zeros after it.

Over billions of years, gravity gathered lots of the universe's gas into stars and planets, and the space in between was left almost empty.

So space is

nearly empty and we're totally stuffed with air.

But why does our air stay here?

One word, gravity.

The same pole that keeps your feet on the ground holds the air down too.

Gravity pulls on air?

But air is so light! How can gravity hold on to something that light?

Because light isn't the same as nothing! Air is made of zillions of tiny invisible bits called molecules, mostly nitrogen and oxygen.

They zoom around like super tiny ping pong balls.

And just like a ping pong ball, each one weighs a teeny bit.

So Earth's gravity pulls on every single little ping pong ball? Every single one! That's what wraps the air around our planet like a giant invisible blanket.

We call that blanket the atmosphere.

Okay, but

when I let go of a balloon, the air rushes right out.

Why doesn't the atmosphere