A fireball is one of the hottest things most people will ever see in the sky, and the rock that survives it is usually cool enough to pick up. Both of those statements are true at once, and the reason is a matter of timing rather than temperature.
The short answer
A freshly fallen meteorite is not hot. The outer surface can be warm to the touch for a short while after landing, and the interior is generally cold, because it has spent millions of years in space and the atmosphere never had time to warm it. Meteorites recovered within minutes of a fall have been described as cool, and in cold conditions they have been found with frost forming on them.
They are also not hot enough to start fires. The UCLA Meteorite Museum states plainly that the surface of a freshly fallen meteorite might be warm to the touch, but is never hot enough to ignite fires on landing. House fires and brush fires attributed to meteorites almost always turn out to have a terrestrial cause.
Why the outside gets hot and the inside does not
The heating during entry is not friction in the everyday sense. A meteoroid enters the atmosphere at many kilometres per second and compresses the air in front of it faster than that air can move aside. Rapid compression raises the air temperature sharply, the way a bicycle pump warms as it is used, and that superheated air melts the outer skin of the rock.
The melted layer does not stay put. It is stripped away as fast as it forms, carrying its heat with it and exposing fresh material underneath, which then melts in turn. This is ablation, and it is why a meteoroid can shed most of its mass on the way down. It is also why the heat never travels inward: the hot material keeps leaving.
By the time a surviving meteoroid has fallen to roughly 20 kilometres altitude, its velocity has dropped to around the speed of sound and it stops glowing. Everything after that point is dark flight, a cold, silent, unlit drop. The rock spends that time being cooled by the surrounding air, not heated by it.
What the measurements show
The reason the heat stays in that thin skin is a physical property that has been measured directly. Meteorites conduct heat poorly. In a study published in Icarus, Opeil, Consolmagno and Britt measured the thermal conductivity of six meteorites across a temperature range from 5 K to 300 K, covering ordinary chondrites, an enstatite chondrite, two carbonaceous chondrites and an iron.
Their iron sample, Campo del Cielo, conducted heat roughly as metallic iron does, rising from about 15 to about 27 watts per metre per kelvin between 100 K and 300 K. The stony samples were a different matter. Their conductivities were governed by the broken, uneven fabric of the rock itself, and came out far below the values for the pure minerals making them up. A stone that conducts heat that poorly cannot pass a brief surface heating event through to its centre.
Opeil C. P., Consolmagno G. J. and Britt D. T. (2010). The thermal conductivity of meteorites: new measurements and analysis. Icarus 208, 449 to 454. doi.org/10.1016/j.icarus.2010.01.021
What witnessed falls record
The clearest evidence comes from falls recovered quickly enough for the condition of the stones to be documented.
The Tagish Lake fall of 18 January 2000 came down on the frozen surface of a lake in northern British Columbia in deep winter. A local resident collected several dozen fragments off the snow-covered ice within days, handling them inside a plastic bag so they were never touched by skin, and they were kept frozen from that point on. Those fragments went on to become some of the most pristine meteoritic material ever studied, and that outcome depended on the stones being cold when they arrived and staying cold afterwards.
Hildebrand A. R., McCausland P. J. A., Brown P. G., Longstaffe F. J., Russell S. D. J., Tagliaferri E., Wacker J. F. and Mazur M. J. (2006). The fall and recovery of the Tagish Lake meteorite. Meteoritics and Planetary Science 41, 407 to 431. doi.org/10.1111/j.1945-5100.2006.tb00471.x
Why the idea persists
The mental image comes from the fireball, and the fireball is genuinely violent. What that image leaves out is the several minutes of dark flight that follow it, which produce no light and no drama and therefore appear in no eyewitness account. The luminous phase is the part people see, so it becomes the whole story.
The wording of the popular account does not help either. A meteor is often described as burning up, which suggests combustion throughout the object. What is actually happening is melting at the surface, and the melt leaves as fast as it appears.
Frequently asked questions
Can you touch a meteorite right after it lands?
Yes, and people have. The surface may be warm and in some cases cold. The reason to avoid bare skin contact is contamination of the specimen for scientific work, not risk to the person handling it.
Do meteorites glow when they land?
No. Glowing stops well before landing, at around 20 kilometres altitude for a typical surviving stone, once the object has slowed to roughly the speed of sound. Everything below that is dark flight.
Can a meteorite start a fire?
The UCLA Meteorite Museum states that freshly fallen meteorites are never hot enough to ignite fires when they land. Fires reported alongside a fireball sighting generally have an unrelated cause.
Why is the inside of a meteorite cold?
Because it was cold to begin with and nothing warmed it. Interiors retain close to their temperature in space during atmospheric passage, and meteorites conduct heat too poorly for a surface event lasting seconds to reach them.
Does the fusion crust prove the rock was hot?
It proves the surface was hot enough to melt, which is above roughly 1,000 degrees Celsius. It also proves how little of the rock was affected, since the crust is generally under one millimetre thick on a stony meteorite.
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