There’s a mysterious audio phenomenon that many meteor observers have reported. As they see the bright object passing overhead in the upper atmosphere, they hear the sounds of popping, hissing and rumbling as if it’s actually nearby. Even a sonic boom from the meteor would take some minutes to get to their ears on the ground, yet these sounds occur simultaneously to their sighting. A new study has solved the mystery with a little help from Alexander Graham Bell. Hello?
Richard Spalding led a team of researchers at Sandia National Laboratories (owned by Lockheed Martin) who published the results of their study recently in the journal Scientific Reports. They found that the first thing most witnesses notice about a meteor is its brightness. They’re brighter than any other object in the sky (sorry Moon) and often the light is pulsating. The second thing many witnesses notice about these pulsing meteors is their heat. Although the streaking space rock is 60 miles or more away, they experience the sensation of heat and that sensation is linked to hearing the sounds of the meteor.
We suggest that each pulse of light can heat the surfaces of natural dielectric transducers. The surfaces rapidly warm and conduct heat into the nearby air, generating pressure waves. A succession of light-pulse-produced pressure waves can then manifest as sound to a nearby observer.
A transducer is an object or device that converts one form of energy to another. For example, an antenna is a transducer because it converts radio waves into electrical signals. “Dielectric” means transmitting electric force without conduction. The “natural dielectric transducers” Spalding refers to are objects around the meteor witness that absorb light from the meteor and conduct it to the surrounding air, generating heat and pressure waves that create the sounds. Common transducers are dark paint, grass, dark clothing and frizzy hair (really!).
This creation of sound from light is known as the photoacoustic effect and only works if the intensity varies by modulating or pulsing. The effect was discovered in 1880 by Alexander Graham Bell, who used it to invent the photophone – the world’s first wireless commutations device to carry voice over light.
What were we talking about? Oh. yeah … meteors. People who hear the sounds of meteors are usually standing near some sort of natural dielectric transducer (a dark wall) or have a head of fine, frizzy hair.
Hair near the ears will create localized sound pressure, so it is likely to be heard. Also, hair has a large surface-to-volume ratio which maximizes sound creation.
If you’re lucky enough to hear the sounds of a meteor, thank Alexander Graham Bell for explaining it. If you hear the meteor say, “Mr. Watson--come here--I want to see you,” use his other invention and call a doctor.