Hot Rock

Meteorites Land Cold, or Maybe a Bit Warm, but They Do Not Land “Hot”

Few meteorites have been collected immediately after they landed on Earth. Frost has been reported on the exterior of some recently fallen meteorites. Many people who have contacted me, however, have used word like “smoking hot,” “extremely hot,” or “too hot to touch.” 

The physics of the process lead scientists to favor cold or, for the smallest meteorites, perhaps a bit warm. “Outer space” is exceedingly cold. As a meteoroid approaches the sun and Earth’s orbit, the sunny side warms a bit, but it does not get hot.

The incandescent (glowing) period of a meteor is only a few seconds as it passes through the upper atmosphere. Although the exterior gets hot enough to melt during the incandescent phase, most of the hot material immediately ablates away (the “tail” of the meteor), so conduction of heat to the inside of the rock is inhibited. Also, rocks are not good conductors of heat.

The passage through the upper atmosphere slows down the meteoroid to the point where it stops glowing about 7 miles above the Earth’s surface. During the minute or so of subsequent “dark fall” the meteoroid is passing through an atmosphere that is not hot.

The interior of a meteorites show no evidence of having been heated during the atmospheric entry process. Meteorites do not burn. Meteorites do not start fires. If you find a hot rock, then it is not a meteorite.

Backscattered-electron image of lunar meteorite PCA 02007. At the top and right is the glassy, vesicular fusion crust that formed on the outside of the meteorite (almost certainly the trailing side as it is several millimeters thick) as it melted during atmospheric entry. Note the sharp contact between the crust and the interior, which did not get hot enough to melt. Image credit: Ryan Zeigler