A meteorite is a piece of space rock or metal that survives atmospheric entry to land on Earth. While the exterior is subjected to extreme temperatures, the object’s interior remains insulated from the heat. This means most meteorites are found at ambient temperature or sometimes even cold. The dramatic visual of a shooting star is an intense but brief event that fails to heat the bulk of the rock.
Heating During Atmospheric Passage
The intense heat generated during a meteor’s descent is not primarily caused by friction. Instead, the incredible speed of the meteoroid causes the air directly in front of the object to be violently compressed. This rapid compression creates a powerful shock wave that superheats the air molecules to temperatures hotter than the surface of the sun. The resulting incandescent layer of superheated, ionized gas, known as plasma, surrounds the falling object.
This hot plasma transfers heat to the meteoroid’s surface, causing it to melt and vaporize in a process called ablation. Ablation is a self-regulating mechanism where the outer layer is continuously shed, carrying heat away from the object. Most small meteoroids are entirely consumed by this process before reaching the ground. The bright streak of light seen across the sky is a visual signature of this atmospheric compression and subsequent ablation.
Why the Core Remains Frozen
Despite the surface reaching melting point, the interior of a meteorite remains insulated. The materials that make up most meteorites, such as rock and metal alloys, are poor thermal conductors. This low conductivity prevents the rapid transfer of heat from the superheated exterior to the inner core.
The duration of the intense heating phase is also extremely short, often lasting only a few seconds to a minute before the meteoroid slows down. This brief exposure is insufficient for the heat to penetrate more than a few millimeters past the surface. As the outer layer melts and vaporizes, it constantly exposes fresh, cold material, further limiting the depth of heat penetration.
Temperature Upon Impact and Recovery
The final temperature of a recovered meteorite is typically at or slightly above the temperature of the surrounding environment. As the meteoroid descends into the denser lower atmosphere, its speed is significantly reduced by atmospheric drag. Once the object slows to its terminal velocity, which is only a few hundred kilometers per hour, the period of intense aerodynamic heating ends.
This transition marks the beginning of “dark flight,” where the object is no longer incandescent. During this phase, the cold upper atmosphere rapidly strips the remaining heat from the thin, melted surface layer. This surface solidifies into a fusion crust, a glassy, dark layer usually less than one millimeter thick, which is a telltale sign of atmospheric passage.
The meteorite may be slightly warm to the touch due to the residual heat of the fusion crust. However, historical accounts of meteorites recovered moments after impact describe objects so cold that moisture from the air condensed and froze on the surface, forming a layer of frost. This freezing effect results from the interior retaining the extremely low temperatures from deep space, which quickly chills the thin exterior once the ablation process stops.