Re: Why can't we hear meteors when they penetrate the atmosphere?

Meteors can and do produce sonic booms at the ground. But in order to do so, they must reach a fairly low height, probably below 20 km or so. Very few meteors get that low; most burn up or explode while they are higher than 80 km. All meteors generate shock waves, but at their typical heights these simply don't have the energy to propagate to the ground. The very thin air is unable to store much acoustic energy, and the sound produced is both attenuated by distance and partly reflected upwards as it moves towards the ground through zones of varying temperature. Many meteors are recorded acoustically by sensitive instruments, however, especially at the very low frequencies called infrasound.

Besides their much greater height, another difference between meteors and airplanes is their size. The intensity of a sonic boom is strongly related to the size of the body generating the shock wave. Most meteors are produced by objects only a few millimeters across. Bright fireballs are produced by objects a few centimeters across. A meteoroid approaching the size of even a small supersonic jet would be very rare indeed.

Meteors that survive to low heights are generally dissipating very large amounts of energy, both as light and sound. Witnesses to these fireballs often report sonic booms, both from the original body and from smaller bodies produced by fragmentation. This latter is often described as sounding like artillery or distant fireworks.

In addition to sonic booms, meteors can produce another kind of sound called electrophonic. While sonic booms are heard a minute or more after the meteor is seen, electrophonic sound is heard at the same time that the meteor is seen. This phenomenon isn't well understood, but presumably involves audio frequency electromagnetic waves formed in the vicinity of the meteor which are converted to sound by metallic objects near the observer. The energy is transported at the speed of light instead of the speed of sound, which is why there is no apparent delay.