Exobase facts for kids

The exobase is the very top part of a planet's atmosphere. Think of it as the boundary where the air becomes extremely thin. Above this level, air particles are so far apart that they rarely bump into each other. This means they can easily escape into space.

What is the Exobase?

The exobase is a special boundary in a planet's atmosphere. It marks the lowest part of the Exosphere. The exosphere is the outermost layer of a planet's atmosphere.

Why is it Important?

The exobase is important because it's where particles start to escape. Below the exobase, air particles crash into each other often. Above it, they can fly freely into space. This is how planets slowly lose some of their atmosphere over time.

Mean Free Path and Scale Height

To understand the exobase, we need two ideas:

• Mean free path: Imagine a tiny air particle. The mean free path is how far it travels before hitting another particle. At the exobase, this distance becomes very long.
• Scale height: This is a measure of how quickly the air pressure drops as you go higher. In simple terms, it shows how "squished" the atmosphere is.

At the exobase, the mean free path of particles is longer than the scale height. This means particles are more likely to fly away than to collide.

The Exosphere

The region above the exobase is called the exosphere. It's the outermost layer of a planet's atmosphere.

• In the exosphere, particles move very fast.
• They can escape the planet's gravity if they are moving fast enough.
• This is why the exobase is sometimes called the "critical level of escape."

Earth's Exobase

On Earth, the exobase is not at a fixed height. It changes depending on the Sun's activity.

• It can be between 500 and 1,000 kilometers (310 to 620 miles) above the Earth's surface.
• During times when the Sun is very active, the atmosphere expands. This pushes the exobase higher up.
• When the Sun is quiet, the atmosphere shrinks, and the exobase is lower.

See also

In Spanish: Termopausa para niños