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Meteors are still very hot when they hit the ground

You'd expect that something heated up so much that it glows would still be hot a couple of minutes later. Actually, the situation is a bit more complicated.

The super-hot air in front of the meteoroid is not actually in contact with the particle. (A particle can still be referred to as a meteoroid as it races through the atmosphere, while "meteor" is meant to describe the whole glowing phenomenon.)

The meteoroid's quick motion sets up a shock wave in the air, like from a supersonic airplane. The shocked air sits in front of the meteoroid, a few centimeters away (depending on the meteoroid's size) in what's called a standoff shock. Between the shocked air and the surface of the meteoroid is a relatively slow-moving pocket of air.

The surface of the meteoroid melts from the heat of the compressed gas in front of it, and the air flowing over it blows off the melted portion in a process called ablation. The meteoroid's high velocity provides the energy for all this heat and light, which rob it of speed. When it falls below the speed of sound, the shock wave vanishes, the heating and ablation stop, and the meteoroid then falls rather slowly, perhaps at a couple of hundred mph (or a few hundred kilometers per hour).

It's still pretty high up in the atmosphere at this point, and takes several minutes to fall to the ground. Remember, this tiny bit of rock spent a long time in space, and the core is pretty cold. Also, the hottest parts were melted and blown off. Even more, the air up there is cold, which chills the rock as well.

All of these things together mean that not only is the rock not hot when it hits the ground, it can actually be very cold. Some meteorites (what a meteoroid is called after it impacts) have actually been found covered in frost!

Meteor Photos and Videos See this fireball from the Leonid meteor shower, plus more videos and 4 photo galleries. And get the early forecast for the 2002 Leonids, set to peak in a stunning display Nov. 19.

Philip Plait is the author of "Bad Astronomy" (Wiley & Sons, 2002). For more about these and other astronomy misconceptions, you can buy his book or visit his Bad Astronomy website.

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