Solar balloons detect strange noises in Earth's stratosphere

Eavesdropping on the skies, researchers from Sandia National Laboratories in New Mexico have discovered mysterious sounds in Earth's stratosphere using giant solar-powered balloons. The balloons carried infrasound recorders up to 70,000 feet and captured sounds like thunder, ocean waves colliding, propeller aircraft, city sounds, suborbital rocket launches, earthquakes, and several unidentified noises. Daniel Bowman, the principal scientist at Sandia National Laboratories, said that some of the mysterious infrasound signals occur a few times per hour during flights, but their source remains unknown.


[Bowman] proposed attaching infrasound recorders to balloons to record the sounds of volcanoes. But then he and his adviser Jonathan Lees of the University of North Carolina, Chapel Hill, "realized that no one had tried to put microphones on stratospheric balloons for half a century, so we pivoted to exploring what this new platform could do," Bowman said. Lees is a professor of Earth, marine and environmental sciences who researches seismology and volcanology.

A recording shared by Bowman from a NASA balloon that circled Antarctica contains infrasound of colliding ocean waves, which sounds like continual sighing. But other crackles and rustling have unknown origins.

In the stratosphere, "there are mysterious infrasound signals that occur a few times per hour on some flights, but the source of these is completely unknown," Bowman said.