The fiery fall through the air

A meteoroid hits the air at tremendous speed. In this lesson you will find out why it glows, why its outside melts and how it slows down before it lands.

Faster than anything on Earth

Meteoroids reach Earth at between about 11 and 72 kilometres every second. Even the slowest is about 40 times faster than a jet airliner.

At that speed, the meteoroid smashes into the air in front of it and squashes it. Squashed air gets extremely hot, so it glows, and the outside of the rock glows with it. That is the meteor you see. Most meteors light up between about 120 and 70 kilometres above the ground, far higher than aeroplanes fly.

Melting on the outside

The heat is so strong that the surface of the rock melts and is blown away. This is called ablation. The inside stays cool because the journey through the air lasts only a few seconds, which is not long enough for the heat to soak in.

In the last moments, a very thin layer of melted rock is left on the outside. It cools and hardens into a dark, shiny or matt skin less than a millimetre thick, called a fusion crust. A fresh fusion crust is one of the best clues that a rock is a meteorite.

Slowing down

The air pushes back on the falling rock. This push is called air resistance, and it is the same force you feel when you hold your hand out of a car window. It slows the rock dramatically.

By the time it has dropped to between about 30 and 10 kilometres above the ground, a small rock has lost almost all its space speed. It stops glowing and falls the rest of the way in the dark, pulled down by gravity, at roughly the speed of a fast car or train. Scientists call this part dark flight. That is why small meteorites usually land with a thud, not a giant explosion.

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