Unexplained, mysterious sounds detected in Earth's stratosphere by solar-powered balloons.

Solar-powered balloons launched into the Earth's stratosphere have recorded a series of mysterious infrasound rumblings that scientists can't explain. The noises, detected by specialized instruments at 70,000 feet above the Earth's surface, have so far defied explanation. The researchers say they will continue to investigate the sounds in the stratosphere, tracing more sounds to their origin points and studying their variability across seasons and different regions of the world.