Ablation
Ablation is the melting and vaporising of a meteoroid's surface as it speeds through the atmosphere.
When a meteoroid enters the atmosphere at many kilometres per second, it rams into air so violently that the air ahead heats to thousands of degrees. The rock's outer surface melts and boils off, and the hot droplets are swept away. This stripping-away process is called ablation, and it is what makes a meteor glow.
Ablation removes most of a meteoroid. Even for meteorites that reach the ground, often only a small fraction of the original mass survives. Because the flight lasts only a few seconds, the heat does not have time to soak into the rock. The inside stays cold, which is why freshly fallen meteorites are not red-hot, and why their ancient minerals are preserved.
The evidence of ablation is written on every fresh meteorite. A thin melted skin, the fusion crust, is the last layer that solidified as the stone slowed. Shallow scooped pits called regmaglypts form where ablation ate unevenly into the surface. The iron meteorites of Sikhote-Alin, which fell in eastern Russia in 1947, show these thumbprint-like pits beautifully.
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Level: Explorer Ages 10 and up