Sandia National Laboratories researcher Richard Spalding, recently deceased, examines the sky through which meteors travel.
So maybe atmospheric shock waves from the meteors are not the cause of the spooky noises
But what if the sounds are caused by the brilliant, pulsating light emitted by the asteroid as it burns up in Earth’s atmosphere?
In an article published Feb. 1 in the journal Scientific Reports, the late Sandia National Laboratories researcher Richard Spalding reasoned that such intense light could suddenly heat the surface of objects many miles away, which in turn heats the surrounding air. This could create sounds near the observer. Colleagues John Tencer, William Sweatt, Ben Conley, Roy Hogan, Mark Boslough and Gigi Gonzales, along with Pavel Spurny from the Astronomical Institute of the Czech Republic, experimentally demonstrated and analyzed that effect.
They found that objects with low conductivity, such as leaves, grass, dark paint and even hair, could rapidly warm and transmit heat into nearby air and generate pressure waves by subtle oscillations that create a variety of sounds. The process is called photoacoustic coupling.
Sounds concurrent with a meteor’s arrival “must be associated with some form of electromagnetic energy generated by the meteor, propagated to the vicinity of the observer and transduced into acoustic waves,” according to the article. “A succession of light-pulse-produced pressure waves can then manifest as sound to a nearby observer.”
This bolide appeared over the Flinders Ranges, in the South Australian desert on the evening of the 24th April 2011.
Credit: Wikimedia Commons
The experimenters exposed several materials, including dark cloths and a wig, to intense pulsing light akin to that produced by a fireball. The process produced faint sounds similar to rustling leaves or faint whispers. Computer models bear out the results.
A less extreme version of the photoacoustic effect had been observed in 1880 by Alexander Graham Bell when, testing the possibilities of light for long-distance phone transmissions, he intermittently interrupted sunlight shining on a variety of materials and noted the sounds produced.
Sandia National Laboratories is a multimission laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies and economic competitiveness.