How can I explain why meteorites are cool when they land?

Question

Accepted Answer

Use the idea of brief surface heating, poor heat conduction into rock, and a slow final fall through cold air; a toasted marshmallow analogy works well.

Pupils often expect meteorites to land glowing hot. Explaining why they are usually cool develops understanding of heat transfer.

Brief heating. The bright phase of a meteor's fall lasts only a few seconds. During that time, intense heat melts the outer surface, but the molten layer is constantly swept away, carrying heat with it. This is called ablation.

Poor conduction. Rock is a poor conductor of heat, so in a few seconds heat penetrates only a millimetre or so. The interior keeps the cold temperature of space, which may be well below freezing.

Slow final fall. Once the meteorite has slowed, usually at 15 to 30 kilometres altitude, it stops glowing and falls the rest of the way at a few hundred kilometres per hour, through air that is often well below 0 °C at high altitude. This dark flight lasts several minutes, cooling the surface further.

Evidence. Many people who have picked up fresh meteorites report that they felt cool or only slightly warm. A few meteorites have reportedly been found with frost forming on their surface.

Analogy. Compare a marshmallow briefly held near a flame: the outside browns or burns, but the middle stays cool. Or consider a baked Alaska, where ice cream survives inside a hot oven for a short time.

Classroom test. Pupils can compare how quickly heat passes through materials, such as metal and stone, by touching the ends of rods warmed at one end in hot water, under supervision. This links to thermal conductivity and insulation.

How can I explain why meteorites are cool when they land?

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