Ask Dr. Universe: It’s a hot transition into Earth’s gravity, caused by friction

Dr. Universe,

Why do things like rockets catch fire as they pass through Earth’s atmosphere?

— Conner, 11, Dunn, N.C.

When objects like spacecraft pass through Earth’s atmosphere, things can really heat up.

To investigate the answer to your question, I talked to my friend Von Walden. He’s a professor and researcher with Washington State University’s Laboratory for Atmospheric Research.

First, he said it helps to know a bit about the differences between Earth’s atmosphere and space.

Our atmosphere is made up of stuff, or matter, called gas. These gases that make up our air include oxygen, nitrogen, carbon dioxide and other elements. But space is pretty empty. There isn’t much matter in-between the planets and stars.

That means when any object travels to Earth from space, it’s going to run into a lot of air molecules. This can create a lot of friction, which is the force of two surfaces sliding against each other.

Maybe you can try to create some friction just by rubbing your hands together. You’ll notice how the motion produces heat, and you can feel some warmth.

As the air molecules in Earth’s atmosphere and the material that makes up the spacecraft push against each other they also create a lot of friction.

At the same time, the air molecules slow down the object such as a returning spacecraft as it passes through the atmosphere at high speeds. In the process, it creates a lot of heat.

There’s so much friction and heat that we can start to see a glow around the spacecraft. It isn’t exactly catching on fire, though.

“It’s like when someone is cooking and the pan turns red or orange. The fire from the stove is heating up that pan, but the pan itself isn’t on fire. It’s the same type of thing,” Walden said.

Astronauts have reported that upon reentry, the glow looks pink and orange from inside the spacecraft. The reentry process only takes about four minutes. After reentry, it’s about a 60-mile journey back to the surface of Earth.

You know, engineers and scientists at places like NASA have calculated just the right angle and speeds at which spacecraft need to enter the atmosphere to make it to space and return home safely. It’s also an important calculation for when we send experiments up to the space station, too.

As a student, Walden even had the chance to send up an experiment on NASA’s Space Shuttle to learn more about how different fluids behave in space.

Whether we send astronauts, experiments, or even everyday citizens to space, the question of what happens to objects when they pass through the Earth’s atmosphere is an important one to think about, especially as we set out to learn more about our solar system.

Who knows, maybe one day you’ll be an engineer or scientist who helps us learn more about space travel. Or maybe you’ll even have a chance to travel to space or another planet as a citizen of Earth.

Have a science question? Ask Dr. Wendy Sue Universe, WSU’s resident science cat and writer, by email at Dr.Universe@wsu.edu.